There are many styles of bike than can be used for general purpose getting around town but they have alternate uses. If your alt use is trail riding, then it makes sense to get an MTB and fit some slick road tyres. You can put knobbly ones on for trail riding.
Other styles of bike would be better suited to alt uses of racing, touring, endurance riding etc.
Assuming you want an MTB, then you need one that is good for general purpose use, and not too specialized for sport riding. For a rider on a tight budget, look for a good used bike with front suspension only and threaded eyelets at the rear for a luggage rack and fenders. Some people prefer rigid, non sus forks for general use.
Make sure it is the right size. Look for crash damage and signs of hard use such as worn transmission (shark's tooth profile cogs).
Any major brand will be good (Trek, Giant, Specialized, GT, etc etc...). Get the best one you can find, something higher up the product line. It will probably be fitted with Shimano components so look for (in rising order of quality) STX, LX, XT grade components.
Buget for helmet, lock, lights and possibly some additional stuff like rack, fenders and luggage system.