Noob time

I did about 5 hours of research, talked to friends who fly a lot, and the Capital One No Hassel Flier card that gives me 1.25 miles per dollar was the one I ended up with.

However I know a lot of people love Amex.

I haven't activated the card yet. Should I cancel and go Amex? Is it a great card that I should keep? Should I get both?

Please advise.