I just bought my first bike a few weeks ago. What I discovered was when I got on "my" bike, I knew it. I tried a Felt, Specialized Ruby, Trek Madone 4.5 and Orbea (I hope I have the spelling right on that). When I got on the Felt, it felt all wrong even though it was fit for me. I got on the Ruby right after that one and it was an amazing difference for me. I knew it was my bike. Because it was expensive and really over my needs, I decided to try another store and tried Trek bikes. I am a weird fit because I have short legs, short arms and a long long body. Peddling penguin. I tried so many bikes in all difference sizes and kept coming back to the Ruby Expert Compact. The last bike I rode was the Orbea. It felt very stiff and there was lots of road vibration. I didn't like the ride although the fit wasn't bad. I got back on the ruby and dug deep into my wallet.

I think you just know your bike when you get on it and ride. Make sure any store lets you take it out on a good ride. Not just in the parking lot.