Air did a good job of synthesizing months of postings on bikes for clydes here:
Clydesdale/Athena Index Thread - read before posting and ALL the old Stickies linked
One thing I don't remember coming up is,
if you are not experienced in bike fitting and all that I would advise going to a LBS.
you don't have a bunch of friends with bikes you can try out to get a good sense about sizing and geometry issues,
They will have several different brands and be able to put you on a bike that fits. (And as was said, they will then be there when you need service.) And they'll usually give you a break on stuff you upgrade when you buy and accessories you get when you buy and they will "service" your bike for X period of time for free. Also, you'll find that the margins are pretty close when all is said and done.
If I were you, I would get an MTB and put slicks on it. (Maybe get two sets of wheels. One for off road with fat knobbies and the appropriate tube) and one for commuting with slicks and the such. You can put reflectors on the commuting wheels and all that stuff... Two sets of wheels will make picking the trail over commuting a lot quicker. (If you do this and the rims are different widths -- this will affect breaking so be mindful of this.)