Mod, please move if I posted this in the wrong area/forum.

I currently have the United MileagePlus Visa Card which earns 1x miles on all purchases but am in search of another credit card that offers a better rate. Correct me if I'm wrong, but is the best the United Club credit card which offers 1.5x on all purchases? Is there any other card out there that offers a better rate on all purchases (not restricted to travel, etc)? The goal is to accrue as many United miles as possible, whether I must transfer them from another rewards program etc.

I also see that the same United Club card is offering a 50,000 miles bonus after $3,000 in purchases. Does this card run any other promotions where I would receive more miles for signing up around this time of year or does it normally remain at a 50k bonus?

Thank you.