If you're exclusively looking to build credit and have little to manage or worry about, I'd suggest signing up for a bank acct at a local credit union, and getting one of their cards. You'll have almost no fees and things will be simple.
If you want more out of your card, given that you'll be paying off the balance, I'd try and find a rewards program you like best. I tend to go for cashback whenever possible.
Credit gets built regardless of what card you get. Whatever you do, beware of rando fees that get tacked on. That's how they make the easiest money.