Another credit card to consider is Aloha Airlines which is issued by First Hawaiian Bank. You accrue 1.5 miles per dollar unlike the one for one of United's and since Aloha is a partner of United, you can use Aloha miles for a United flight. It would take $26,250 (as opposed to $35,000) for a domestic flight.

But I agree with others that earning miles by credit card takes a long time and unless you're a big spender (like buying a new car and charging it) or you're getting married in a few years rather than a few months, you may want to pay for one fare and use the miles for a companion ticket.

Congrats!