We live a 2.5 hour flight away from DHs family and really need to make more of an effort to visit. We're looking into getting a credit card where we can build up miles to use for these trips, but it's really hard to compare them all. We prefer to fly Southwest, but aren't sure we want a dedicated southwest credit card.

What card to you have to accumulate airline credits? Is it specific to one airline or can you use it anywhere?