I'm completely new to bikes, but I've been doing some research before my first "real" bike purchase. What I'm looking for is the best value for my needs.

After some extensive research among various brands, I've narrowed my choices down to the Trek DS Series, as I will be using the bike to commute nearly every day from class to class (1-5 miles/day). It will be mostly road but I shied away from the FX series as I may be taking it offroad on occasion.

That being said, I have three options I'm considering:

2012 Trek DS 8.2 - $477
2013 Trek DS 8.3 - $710
2012 Trek DS 8.4 - $805

What I know is that the 8.4 has hydraulic disc brakes, which I don't know if I'm competent enough to maintain; the 8.3 has mechanical disc brakes; and the 8.2 doesn't have disc brakes.

I would like to use this bike for at least the next 3 years, so I'm impartial for choosing the cheapest one. I will probably test drive all of them at my local bike shop, but I'd appreciate any input I can get from you guys beforehand

Thanks!