Originally Posted by Nicodemus
Since you are mainly commuting and also want to do a bit of cardio training, you may find that you're on roads much more often, in which case checking out something like a Specialised Sirrus might be worth looking at as well.
I agree generally with cyccocommute, though don't stress so heavily on the 'purity' of different bicycle breeds (I think that came out wrong, don't mean to imply you're into bicyclic cleansing or anything). I'm also not sure how useful talking about a 'stable' of bikes will be to a newb who just wants a good all-rounder. Hybrids have their place and shouldn't be so readily derided, however I do agree that if you're going to end up using a bike much more for one thing than another, it's best to get a bike more suited to that purpose.
I have a Sirrus and it's great. For me, it's mainly solid and sturdy, with tires that are reasonably thin and fast but no so extreme as a pure racing bike. And I prefer the straight handlebars for the myriad uses I have for the bike. I'm not some kind of "half-breed" hybrid freak, am I?
Sure, hybrids have their place but I'm just not sure where that is. Most of the people that I've ridden with who have hybrids eventually ditch them for either a mountain bike or a road bike depending in which way they lean. Sometimes both. When people ask me for advice, I usually steer them toward a hard tail because it's the ultimate "go any where" bike. Sure it can be kind of slow on the road but most people aren't racing. And it may be a little rougher off-road then a long travel dualy but it's also lighter and, at a lower price, a better bike.
And then there is the "grin" factor. Take a road bike out and ride it and it's just exercise (over simplification). Take a hybrid on more than dirt roads and you can see fear in their eyes. Take some one out in the woods on say, the Colorado Trail...very doable real single track, and they come back with mud in their teeth from grinning so much. They're fun bikes! They're the bike you wanted when you were 10 and couldn't afford. You just don't hear other bicyclists whooping it up as much as you do a group of mountain bikers. And if it's fun, people will ride more which, after all, is the point, isn't it?