Theyre very similar phones.
With s20 FE you get newer processor and 5G support plus 120hz display plus a larger overall display size
With S10 you get a better and higher resolution screen, and 2GB more ram on 128 model (FE has has 6GB on the 128gb model), lighter weight and headphone jack if that’s important, and an ultrasonic finger print scanner in display (FE has optical finger print scanner, not Ultrasonic)
I think if they’re the same, I’d go with the FE just because Samsung now supports phones for 3 major updates...unless you plan on upgrading before that, the FE has one more cycle than the S10
Both are great though. This is assuming you can get both for same price. If S10 is cheaper I’d stick with it, but if you can exchange it for FE I would do that