Originally Posted by
AzTallRider
Don't just ride each one a little longer; take each one for good ride. And push the LBS if you have to, to get each one set up as for you as well as they can. Make sure your test includes a hill, so you can see how it feels standing up and climbing. Do some all out efforts on each bike to see how that feels. Do some slow tight turns, and do some fast turns. Pay really close attention to how the bike is responding to you during all this, and how it makes you feel. So long as each of them can be tweaked to fit you properly, choose the one that makes you feel the best riding it. That includes how you feel about the looks.
This also tests some very important things: how well the LBS will work with you, and how much skill they have at getting you set up properly. For a newbie (and maybe for an oldbie too!) these are very important things. You should be able to have a relationship with the bike shop folks. It'll pay off as you grow.
If you're going to spread your wings and fly, they are your ground crew, at least until you can do your own adjusting and wrenching.