Most of my LCC experience is a few years old, but here you go:

Southwest - I try to avoid them at all cost. Most of the really bad was in boarding and connecting.

Frontier - was not bad and would consider them if none of my regular options were available.

Spirit - aside from the lack of customer service and difficult to apply FF program, my big seat up fronte from MCO to FLL. was fine

US - It is what it is. I have just lowered my expectations when I fly them so I am less frustrated with them now.

I would like to try JetBlue sometime.

I am afraid to do the AirTran thing.