Since that's the case, it looks like the biggest difference between the two is that the Nirvana has 700c rims (road bike size) while the Trek has 26-inch rims (mountain bike size). That, and the fact that the Nirvana has a suspension seatpost.

In my opinion, the suspension seatpost isn't necessary and should probably be avoided. You could easily swap it out, though, if you decide that you'd prefer to have 700c wheels vs. 26-inch wheels. For the kind of riding it sounds like you'll be doing, either wheel size would work fine.