Avoid Allegiant Airlines. They removed the padding on the seats so they could get in a couple of extra rows. The seats don’t recline and the tray tables are exactly as big as an iPad. My knees touch the seat in front and I’m only 5’10” tall. After three and a half hours sitting on the rock hard seat, I was not feeling very charitable toward them.
We just flew on Frontier. It wasn’t too bad. The seats don’t recline but that can work both ways.