If there was a best bike, we'd all be riding it. Once you get out of the absolute crap category, all modern bikes are very good, the differences between comparable bikes are mostly preference. Do you prefer sharp handling, or a more stable feel? That kind of thing.
For your needs I'd be looking at aero tubed racing bikes. You don't need 40 mm tire clearance in a tri. You don't need Future Shock or anything to ride for an hour. Etc.
Most of what makes a bike fast is the rider. Whatever you go with, plan to spend about $75 per tire immediately. Maybe you'll get a better deal, but put that in your budget in case you don't. It's amazing how much difference tires make.