I think the key thing as others mentioned is the ability to mount fenders and a rack. I look for this more than anything when I consider a bike. I have touring / cyclocross / hybrid frames that all have lots of clearance and braze-ons. From there, ride drops, bullhorns, flat bars whatever. As others stated you can get aero with anything by adjusting the stem and bars. My Hybrid stem is pointing down due to the crazy tall headtube but ultimately it puts me at the same height as I am on a road bike. I use flat bars with no rise as well and I shoved my brake / shifters as close to the center as they could go to reduce the width of the bars effectively.

In the end, I am just saying bars can be swapped and adjusted... best make sure you have a frame that works as a first order of business. Next thing to consider is what kind of shifters you like - if it is brifters (my preference) you best buy a bike that has them as switching out bars later is a costly endeavor. Also, make sure to go with a 8 or 9 speed system only. 10 speed is far more expensive for little gain - just look at the price of a chain...