Well, I also dated two Catholics (the second of which I married) and no protestants. I ended up breaking up with the first mainly because he was Catholic. (I was shamefully ignorant then.)
In the church that I attended and when I attented Liberty University, Jerry Falwell’s school, I found that many protestant guys tended toward rebelliousness. The one guy from my protestant church that I ever considered attractive at all ended up getting heavily into drinking and partying at college. My observations of young protestant guys has led me to believe that perhaps their parents strive too hard to keep them cut off from anything non christian and so they very, very often end up rebelling. This is true of my younger brother among many others. I find that rebellious nature distinctly unattractive.
Instead I fell in love with an intelligent and mature guy who was secure in his beliefs. (The Catholicism was incidental, really.) We had alot of explosive religious arguments in the beginning. But that was mostly because he had an annoying tendency to calmly and logically prove me wrong again and again.