So I'm in the market for a new bicycle. Haven't ridden one since high school, so I'm re-learning everything. I plan on doing mostly pavement riding, but also the occasional dirt/gravel road. No hard core mt biking at the moment, maybe light trails. I'm 6'1'', and now at 240, but going down, so I need a decent sized bike. I want to spend around $500-600. I have been trying to decide between a hybrid and a mt bike.

I have two that I like, and am asking for input. My logic goes like this:

Trek 3700 Disc - Bicycle Garage Indy - Indianapolis and Greenwood, IN

With this Trek, I can buy a set of tires that are more suitable for the pavement, but also capable of going "off'-road". The bike itself is off-road capable, but would it be comfortable for longer pavement rides? The fork locks, which would help.

Giant Roam 3 - Bicycle Garage Indy - Indianapolis and Greenwood, IN

This hybrid seems more suited for the road, but would it be able to handle any off-road scenarios? The tires seem dual purpose, but I think it may struggle of-road.

One thing to mention, I signed up for a mini-triathlon. The riding section is 13 miles, and I plan to train and use whatever bike I get. But I also want to be able to take it out and casually ride with it.

any input is greatly appreciated...like I said, I'm just beginning to look. I plan on going an talking to someone this weekend, but want to have some idea before I go.

Thanks