People ask me all the time about credit cards and how to choose them. If you're looking to choose one and you absolutely love to travel like I do, here's a list of what each one offers you. Please note this does not mean you use your cards as a way to get access to spending money you don't have; you would have to be able to pay off your statement balance each month.
My personal opinion is that you should first look at:
1) the places you want to go to more often
2) see what airlines offer the best prices on a consistent basis
3) choose the card that is exclusive to that particular airline
I personally have four credit cards from different airlines (Jetblue/Southwest for travel within the US and American/Delta for travel outside of the US) and without question, the majority of the trips I take are done by using points. Enjoy!