For a first bike in your situation I'd look for something inexpensive and used that fits decently. The type of bike may not make much of a difference: road, mountain, hybrid. Get out and start riding. Once you've got a bit under your belt you might find a club in your area that offers suitable rides. After some months you'll have a better idea of what type of riding and what type of bike you might enjoy.

If you do buy used either go through the bike yourself and get a tune-up at an LBS. It's discouraging to experience breakdowns when you're just trying to get started.