Vote # 3 for the mountain bike

You mention getting "into" mountain biking. To me that says "single track" and single track includes roots, rocks and logs. You'll need the slightly more agressive position and narrower saddle available on a "real" mountain bike.

Modern hybrids generally put the rider in an upright position and include comfort features such as suspension seatposts, upright handlbars and big cushy seats. They are great for coffee runs in town, pulling the kids in a trailer on the bike path, and as beginner "road" bikes for people who want to try longish distance road-rides with-out the road-bike price