For me it depends on the scenario.
I use WD 40 1st. It's cheap, cleans up easy and works fine. If that isn't working, rarely, I do have 50% acetone & 50% trans fluid mixed up and ready to go. I only use this if I can't heat it up and have some time.
If I'm in a hurry, and it's a common fastener, it's either going to come apart or break. Either is fine.