I have only had my Roubaix Comp with Rival for a bit over a week now, but I am very happy with it. I test road 105 and Rival bikes. Although as a newbie I am sure I would of been happy with either, I liked the Rival just a bit more. I like the clean look (new 105 has this as well, but I didn't want to wait for a 2011 bike). And I liked the double tap as well.

I agree with others, ride both until you know what you want and go from there. When I was first shopping I only wanted 105, glad I tried the Rival.