Originally Posted by Portis
A mountain bike is an excellent place to start. It will allow you to go on paved roads, unpaved roads and off road. No other bikes are good at all of those. It won't be long after you buy, that you will decide what really appeals to you, but there is only one way to find out.
In response to the red wors: Actually, certain types of road bikes can be pretty decent off road. Like cyclocross bikes, and even certain touring bikes. However both of those are out of this price range, so I agree that a mountain bike will be best. Both on road and off road it will be faster than the hybrid, unless the hybrid is of Trek's FX series, which are road oriented (but not great at off road).
That'll be enough trolling from me, sorry.
I'd say go for the best mountain bike you can afford. It will last you a long time, probably. Just budget in a pair of tires for road use. Happy trails (roads?)