Amex cards (not Delta Amex). Maybe those bonuses are only for business cards, but just get one of those. Take your pick. I'd take the Platinum if the bonus is significantly higher. (I picked up a gold yesterday, already have Platinum for me and wife). You'll get sky club access when you are flying Delta and other perks.

You can transfer the miles to Delta if you choose or you can redeem them for flights on the portal or transfer them to other airlines. That makes them much more valuable than Delta miles