Thomas Cook, TUI, JET2, VS, BA, RYR. I would guess that TC is the biggest UK pilot employer at MAN. MAN is the UK HQ. Company seems to be centralising the operation to fewer bigger bases with MAN being the largest by far. Jet2 have expanded recently too. TUI are/have been recruiting for UK bases, but I don't know if MAN is on offer.
As regards working at MAN, much the same as everywhere else. Parking is currently a major pain due to airport expansion, don't see that changing. Security has improved to a standard where it doesn't stress you too much. If you do come fresh to MAN consider carefully where you live, the road network from the SW and NW is a daily nightmare. Closer to the staff carpark the better.