ok, i'll champion trek. people might feel they "sold out" or are a big evil corporation (both true to a certain extent) but fact is, they make damn good bikes. they have the bazillions of dollars for research to make the damn good bikes they make. Trek bought out Garry Fischer, so gary puts his name on the bike but trek makes them. good bikes, don't bother worrying about the name on them. trek/gf/ all the same.

the 4300 is a good solid bicycle that will last you many many years and is worth the price.
for your son, have you thought about the 7.2 FX? if he is riding mostly on the road, it might be a good choice for him.
if the bikes are comfortable, and they are in your price range, then go for it.
try as many bikes as you can and get the ones you can afford that feel the most comfortable. good luck.

(just so you know where i'm coming from, i don't ride trek at all. but my friend who is a super badass rides and swears by them. he rode his trek remedy on the centurion, 100+ miles of mountain bike trails in moab in under 24 hours. if trek is good enough for him, it should be good enough for most. we just recently started carrying trek, but my support for them has nothing to do with it. my wife currently rides a Trek 820 that she has had for 15 years. trek was my first mountain bike.)