I was literally down to these exact two choices OP. I test drove both extensively. I ended up with the Mazda3 Sport Hatch with the Premium Package, but I'll help you as best as I can.
Note that to match (and slightly exceed) a fully loaded Mazda3 hatch in terms of features (approx $32.5k + tax), the A-class will cost at least $50k+. That being said, the A-class does have much deeper factory discounts than the Mazda3 (the nearby Merc dealer to me is offering $5k off pre-negotiation). Mazda's not giving much on the Mazda3, any discount you get will have to be negotiated hard at the dealer. So the gap depending on where you are might be "only" 11-15k. But thats if you care about all the features a fully-loaded Mazda3 offers.
In terms of power/acceleration, the Mercedes has more torque so off the line it feels noticeably stronger and smoother, but not ludicrously stronger. 0-100 they're not as far off as you'd expect for the difference in price - Car and Driver has the Mazda3 at 7sec, A250 according to Mercedes is 6.1 seconds. That being said in Sport mode the Mazda3 is more than enough for anyone. Handling wise, both are very good, the Merc is better IMO. More planted and surefooted than the Mazda3, but the Mazda3 is still very good for its segment. Far better than my 2012 Ford Focus. As far as noise control goes, both are the same in terms of loudness IMO. Both control wind noise well, but there's a definite road noise from the tires.
In terms of interior niceness, honestly.........the Merc is not actuallllly nicer than the Mazda3. Yup, I'm saying it. The only two things the Merc has that you can call a definitive win are the 2 massive 10-inch screens at the front, and the pano sunroof. Amazing screens, probably best in market right now. But aside from that, I honestly cannot say that the rest of the cabin materials is nicer. The Mazda3 has leather all a big portion of the dash whereas the Merc has bad piano black plastic, and anywhere else the Mercedes has leather, so does the Mazda. The actual design of the cabin the Mazda wins IMO, there's so much style to it whereas the Mercedes is more flashy and gaudy. At night it's like a crazy nightclub in the Merc whereas the Mazda is kinda dark and dreary, even during the day, so the Merc wins there if that's your style. Its something you have to experience to believe. That being said in terms of a coherent design, I think the Mazda wins. The Merc in no shape or form is worth $10-$15k more when it comes to the interior quality.
The A250 is more practical than the Mazda3 for sure, despite being very similar dimensions on the outside. More passenger room overall, way brighter in the A250 whereas the Mazda3 is like a dark cave especially at the back. The Merc does have rear AC vents in the back, which could be important if you carry lots of passengers. More cargo space in the A250. 40/20/40 split for the rear seats, if you go skiing that's absolutely amazing. Another thing - the Mazda3 hatch DOES NOT come with a button on the remote keyfob to open the trunk at ANY price! You have to open it with your hands every time. Whereas the A250 has the button plus you can wave your foot to open the trunk. So much more convenient there.
As for exterior style...if you can get over the ugly C-pillar of the Mazda3 hatch and the weird way the rear of the hatch suddenly ends, the Mazda3 can be very gorgeous. Colour is personal pref but I think the Mazda3 needs to be in Red or Polymetal to really shine. The rest of the colours are meh. The A250 style is solid IF you get the Sport/Night package, you can't call it ugly, it doesnt have the ridiculous c-pillar of the Mazda3, but it's not necessarily outstanding either.
Feature-wise, the Merc can have every feature the Mazda3 has, and then some, if you're willing to pay (except for the heads-up display, can't get it on the Merc in Canada from what I understand). But the Merc will have the aforementioned trunk button and foot release, better voice commands with Hey Mercedes (but honestly...once you learn the Mazda voice control system or use android auto, the Mazda3 is good enough - unless you really are too lazy to turn the temperature knob with your fingers..)
Insurance + gas-wise the Merc will cost more but not substantially more. I'm sure maintenance will cost more. Reliability....who knows but my money's on Mazda.
In summary, I ended up going the Mazda3 because frankly, I couldn't justify the extra $10-$15k. I wanted to so bad, and part of me still does, but I can't. I am honestly very happy with the Mazda3. There is some bizarre costcutting in the Mazda (no trunk remote release, no pano sunroof, cargo area doesn't have storage nooks, no rear AC vents) but if those things aren't deal breakers and you're not fixated on the MB badge then save the money and get the Mazda3. If you want an overall "better" vehicle and money's no object, then get the MB, it is objectively a great car. People love to trash the A-class but they're honestly full of s***, can't afford an A-class, or havent actually driven one. Every pro review on the A-class is extremely positive (same with the Mazda3)
Note that to match (and slightly exceed) a fully loaded Mazda3 hatch in terms of features (approx $32.5k + tax), the A-class will cost at least $50k+. That being said, the A-class does have much deeper factory discounts than the Mazda3 (the nearby Merc dealer to me is offering $5k off pre-negotiation). Mazda's not giving much on the Mazda3, any discount you get will have to be negotiated hard at the dealer. So the gap depending on where you are might be "only" 11-15k. But thats if you care about all the features a fully-loaded Mazda3 offers.
In terms of power/acceleration, the Mercedes has more torque so off the line it feels noticeably stronger and smoother, but not ludicrously stronger. 0-100 they're not as far off as you'd expect for the difference in price - Car and Driver has the Mazda3 at 7sec, A250 according to Mercedes is 6.1 seconds. That being said in Sport mode the Mazda3 is more than enough for anyone. Handling wise, both are very good, the Merc is better IMO. More planted and surefooted than the Mazda3, but the Mazda3 is still very good for its segment. Far better than my 2012 Ford Focus. As far as noise control goes, both are the same in terms of loudness IMO. Both control wind noise well, but there's a definite road noise from the tires.
In terms of interior niceness, honestly.........the Merc is not actuallllly nicer than the Mazda3. Yup, I'm saying it. The only two things the Merc has that you can call a definitive win are the 2 massive 10-inch screens at the front, and the pano sunroof. Amazing screens, probably best in market right now. But aside from that, I honestly cannot say that the rest of the cabin materials is nicer. The Mazda3 has leather all a big portion of the dash whereas the Merc has bad piano black plastic, and anywhere else the Mercedes has leather, so does the Mazda. The actual design of the cabin the Mazda wins IMO, there's so much style to it whereas the Mercedes is more flashy and gaudy. At night it's like a crazy nightclub in the Merc whereas the Mazda is kinda dark and dreary, even during the day, so the Merc wins there if that's your style. Its something you have to experience to believe. That being said in terms of a coherent design, I think the Mazda wins. The Merc in no shape or form is worth $10-$15k more when it comes to the interior quality.
The A250 is more practical than the Mazda3 for sure, despite being very similar dimensions on the outside. More passenger room overall, way brighter in the A250 whereas the Mazda3 is like a dark cave especially at the back. The Merc does have rear AC vents in the back, which could be important if you carry lots of passengers. More cargo space in the A250. 40/20/40 split for the rear seats, if you go skiing that's absolutely amazing. Another thing - the Mazda3 hatch DOES NOT come with a button on the remote keyfob to open the trunk at ANY price! You have to open it with your hands every time. Whereas the A250 has the button plus you can wave your foot to open the trunk. So much more convenient there.
As for exterior style...if you can get over the ugly C-pillar of the Mazda3 hatch and the weird way the rear of the hatch suddenly ends, the Mazda3 can be very gorgeous. Colour is personal pref but I think the Mazda3 needs to be in Red or Polymetal to really shine. The rest of the colours are meh. The A250 style is solid IF you get the Sport/Night package, you can't call it ugly, it doesnt have the ridiculous c-pillar of the Mazda3, but it's not necessarily outstanding either.
Feature-wise, the Merc can have every feature the Mazda3 has, and then some, if you're willing to pay (except for the heads-up display, can't get it on the Merc in Canada from what I understand). But the Merc will have the aforementioned trunk button and foot release, better voice commands with Hey Mercedes (but honestly...once you learn the Mazda voice control system or use android auto, the Mazda3 is good enough - unless you really are too lazy to turn the temperature knob with your fingers..)
Insurance + gas-wise the Merc will cost more but not substantially more. I'm sure maintenance will cost more. Reliability....who knows but my money's on Mazda.
In summary, I ended up going the Mazda3 because frankly, I couldn't justify the extra $10-$15k. I wanted to so bad, and part of me still does, but I can't. I am honestly very happy with the Mazda3. There is some bizarre costcutting in the Mazda (no trunk remote release, no pano sunroof, cargo area doesn't have storage nooks, no rear AC vents) but if those things aren't deal breakers and you're not fixated on the MB badge then save the money and get the Mazda3. If you want an overall "better" vehicle and money's no object, then get the MB, it is objectively a great car. People love to trash the A-class but they're honestly full of s***, can't afford an A-class, or havent actually driven one. Every pro review on the A-class is extremely positive (same with the Mazda3)
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