Alright guys, I need some help. I'm in the market for lower end hardtail with a budget of absolute tops of $600, this includes such things as a new helmet, locks, and other minor stuff.. so the bike budget is about $500. I plan to commute on the bike to and from school when it isnt pouring too badly out and riding around town occasionally. I'm interested in getting something capable of handling trails great as its something that I'm interested in doing here and there. No I won't be doing 4 foot drops and what have you. I have called around and narrowed my choices down to these four bikes:

Marin Bobcat trail
I called and I can get this for around $460, maybe less.
This is the most appealing of the bikes I have narrowed it down to as its got fairly conservative styling, I don't want attention. I can't afford to have my bike stolen. It has disc brakes despite being a sub $500 bike but this is something I really want.

Specialized hardrock sport 06
Calling around and looking online, I should be able to get this for under $350. I like the styling of the bike but I'm not crazy about leaving a specialized bike locked up around here in some parts of town.

Specialized hardrock comp 05
A shop somewhat around here has them going for something like $430. I like the disc brakes on this one and whatnot but I'm not too crazy about the paintjob and what have you.

Marin bolinas ridge
Clearly the cheapest bike of the bunch. Its got the somewhat conservative "wtf is a marin bike" thing going for it which I like. I'm fond of darker paintjobs but I would budge. I'm pretty sure this can be upgraded to disc brakes at a later time also.

My current bike was a used department store wannabe fs piece of ****.