UA and the Barclay Arrival card are two of the best choices. Go for those and then see what else you might want to add as time goes on. Keep reading, and the information overload factor will decrease. If Southwest serves your airport, I would get one or two Southwest cards when the bonus is 50K.

You can use any airline (even award taxes and fees), any hotel, any car rental agency or any online travel agency with the Arrival card, and you have 90 days to redeem. So you can actually earn all the points to cover a charge after making it.

Assuming award seats are available on UA, you will get more out your UR by transferring to UA (or Southwest) than you would redeeming through the UR mall.