What kind of bicycle should I purchase?

You answered your own question by stating, "i will mainly need the bike to commute to school which it has some rough trails and i would also like to ride it for fitness purposes as well (parks, NYC bike tour)." There's one type of bike that can handle rough city trails & can be used to commute & be used for fitness & can be used for touring & can be used for just about anything in or around a city...a "touring road bike". I doubt you can afford it. $1,200 for my 2011 Raleigh. Most likely about the same price for the 2012. Link below. One tough son-of-a-b**** bicycle, with extra amenities such as real leather wrapped handlebar - real Brooks Aged Leather B-17 saddle - fenders - spare spokes mounted on the right side chain-stay - Lezyne Road Drive Frame Pump, etc., etc.

If it is rough trail, forget the road bike (unless you want to get a cyclo cross bike, which is mondo bucks) and forget the fixie. So you are down to MTB or hybrid. A MTB sucks on road. It sounds like you are in a more urban setting, so I think a hybrid is the choice. If it is rough trail, you might try a hybrid with front shock. If you can live with getting bounced around, then a hybrid without a front shock. The front shock is useless on road, but you have to gauge the road vrs. what your bike is capable.

If you look at mountain bikes be sure to see the price point to get lock out shocks. That way you can twist or flick a lever and ride like a rigid fork on pavement. I think a flat bar road bike with a pair of Schwalbe Marathons 700 x 32 (or) 35 would be my choice for your task. Now if the gravel is course loose stone and the trail has lots of obstacles that mountain bike looks better. Buy a U-Lock and a cable lock and use them both every day. Plenty of answers you can search here on how to lock a bike. You do want to keep your new bike, right?

Hey Stephen, No... I won't cut you any slack ;>) Best advice I can give you is go to your local bike shop(s) and tell the folks there what you'll be doing with the bike and what your price range is. They'll most likely have different bikes that you can test ride and get a better feel for what it is you're looking for. Personally? I have 3 different bikes, a single speed, a dedicated touring bike and one I built from the frame up at a local bike co-op. I live in San Francisco and I ride them all. I am kinda partial to the one I built up though.

Steven You buy a bike based upon where, and how you will ride. The tough part you specify is how 'rough' the trail will be. If it is mtn bike tough, unless you want to go around it, then a mtn bike is your answer. It is however, not the best choice for long distance, fast riding, tour or fitness rides. For that you will want a road bike. Your call. Soccerref

Mountain and fixed gear bikes are out. You want a hybrid, touring, or cyclocross bike. All 3 will handle gravel bike paths with the touring bike being the best for bike tours. Touring bikes will be more comfortable and have stronger wheels and wider tires and can go about everywhere. They are also $1,000 and up. Fit is very important so visit the local bike shop. http://www.rei.com/category/4500922

cyclocross they can take wider tires than a reg road bike but are still nice for road [esp if you change the tires to skinnies for a road trip] ALTHOUGH 'schools' can be hotbeds of bike theft maybe get something used that is decent, make it ugly, use a good lock, park in unexpected locations wle

Get a hard tail mountain bike. They are good for both roads, and rough trails. You won't be doing any jumps with them though, as most of them are pretty heavy. I have a trek 820 that I've been happy with for over 3 years.

I've been riding the trails a lot lately, this mild east coast winter weather is a dream come true! Try HARO BMX BIKES. http://www.bike-trailer-reviews.org/