Your size is borderline for larger 700c wheels, and if you want to ride anything technical, you will find smaller wheels easier to handle. Go with 26" MTB wheels, but fit a mixed use tyre with a continuous tread. Knobbly tryres suck on the road.

I would suggest an MTB with a quality fixed fork . These are much more comfortable than cheapo steel forks on low-end bikes. You can use a suspension front fork if you want, but it will add weight and maintainance.

Pick the right sized bike, one with plenty of standover height, and not too long from saddle to bars. Make sure the cranks (bits of metal with pedals at the end) are on the short side. Try and get 165mm length, not 170mm, and definately avoid 175, which seems to be standard on many MTBS.

Pick a frame of butted steel or aluminium, with threaded eyelets for fitting a luggage rack and fenders. Even if you dont use them right now, one day you will.

Jamis makes some well designed bikes at good prices.
See
http://www.jamisbikes.com/hardtails_intro01.html