I recently went through the same dilema, wanted to get into biking to lose weight. At the time I had an older mountain bike with no suspension. My friends that had bikes all had mountain bikes with suspension. So I decided to get a mountain bike with full suspension, figuring it would be more fun to ride with it and naturally getting something new and as expensive a a full suspension mountain bike would get my butt off the couch and riding. Well after riding in the woods with my buddies for a few weeks and the thrill of having a new bike wore off, I wasn't riding in the woods as much. So I decided to get a second set of wheels with road slicks. This got me out riding more, but still not as much as I needed to be riding to shed some of the layers I've put on over the years. This all happened last fall. So then winter came, I bought a spinner, and some spinerval videos. Used it a handful of times over the winter. So spring comes, and got into a little kick where I rode my bike for a week or two here and there. So I decided about two and a half months ago to get a rode bike, since that is all I used my mountain bike for anyway. Best decision I could've made. I'm totally addicted to riding now. I've ridden my road bike more times and probably more miles in the past 2.5 months than I did all year on my mountain bike. Road riding, for me anyway, is much easier to gage your progress. You start out only being about to do a certain amount of miles, and struggle making it up some of the hills, and before you know it, you are cruising up the hills at a pretty good clip, and the short rides you started off with are to short. It is completely addicting, I think about riding all day now, since I got my road bike, can't wait to get home from work and ride it. I've even ridden my spinner more times already this year(due to bad weather) than I did all winter last year. So my advice to you is go for the road bike, this is only in my opinion. I think mountain biking is a lot of fun, I still plan on going sometimes, but the thing is, depending on where you live, you normally have to put the bike on the car and drive somewhere to ride. With a road bike you open up the garage door and you are off. Sorry for the long post, but I just wanted to throw in my two sense.....