I'm not even exaggerating or being a wise-guy here - you will likely find multiple bikes that work for your parameters of budget and size/needs. They will all be sufficiently similar that aside from egregiously bad fits, there will be no way to objectively tell or predict which one will work better for you.

Make the final choice on looks. Seriously. That's the biggest real difference between bikes in a similar price range at the LBS. Once you get into a similar price category, unless you're looking at specialty hi-end bikes, the components, parts, etc. will all be of very similar quality and level.

The last advice - even though you can ride for the rest of your life on entry-level stuff without limitation, almost all cyclists get upgraditis sooner rather than later. One of the best money saving moves I've made in (this expensive sport) of cycling was to buy a Cervelo as my first bike. Seemed like a splurge at the time, but I knew I'd be riding pretty seriously and 5 years later, not needing to upgrade has probably saved a fair amount of money.

I did still buy a $650 entry level bike for commuting though, and when I ride it, I never think "wow my Cervelo is so much of a smoother or faster ride." It's not. The $650 bike rides really, really well, and the triple is helpful for big climbs. The Cervelo gets more of the "wow" factor but looks aside, I consider them equal in terms of performance despite the fact that the Cervelo costed 4x the Giant.