Air Conditioner Installation Choices

So I obtained 3 quotes for an AC install in my ~2500 sq. ft house (2 years old, all hardwood) from Home Depot (contracted out to Compass Home Services), Costco (contracted out to Limcan Walker/Certified) and Reliance. Regardless of who I end up going with, I will need a either a concrete slab/pad or angle brackets to support the AC as they would need to install it on the side of my house, which is sloped.

Please help me decide which is the best option? Also, do I really need a humidifier to be installed inline my furnace output duct (i.e is this useful for winter if my house is all hardwood)?
I have a vigor HRV residential air exchanger already installed in my home.

1. Home Depot (contracted out to Compass Home Services)

*Ameristar (14.5 SEER, 10 yrs parts + labour), $3884 + HST or $121.91 x 36 months @ 0% interest - $250 OPA Rebate

*Trane XR13 (14.75 SEER, 10 yrs parts + labour), $3977 + HST or $124 x 36 months @ 0% interest

*Trane XR14 (16 SEER, 10 yrs parts + labour), $4766 + HST or $149.91 x 36 months @ 0% interest - $400 OPA Rebate


2. Costco (contracted out to Limcan Walker/Certified)

*Lennox XC14 (up to 16 SEER), $5299 + HST - [Costco Cash Card ($500) + Costco 2% Cash Back ($106) + OPA Rebate ($250)]

*Lennox XC13 (up to 15.5 SEER), $4049 + HST - [Costco Cash Card ($400) + Costco 2% Cash Back ($81) + OPA Rebate ($250)]

*Humidifier, $400

3. Reliance Home Comfort

*Smart Air 1000 AC (Rheem or Carrier, 16 SEER), $3900 (10 yrs parts + labour) or $3300 (5 yrs parts + labour) - OPA Rebate ($250)
*Humidifier, $400

OR

*Smart Air 1000 AC (Rheem or Carrier, 16 SEER), $55.99 per month x 7 years - OPA Rebate ($250)
*Humidifier = Free
*Protection Plan for furnace, Yearly maintenance check on furnace and AC, and 1 month free billing