Ryanair should never be a consideration because of its super-crappy management. Sure, the roster is stable and the 800 is a very nice aircraft, but you never know what the whacky CEO will do next... He's a big jerk among jerky airline CEOs...
If you want to continue to fly the 777, then choose BA - but you likely won't upgrade for at least a decade or so...
I'd say go with Thomsonfly. Nice destinations on the 737 and you can eventually get into a comfortable 757/767. Not too shabby...
Good luck and let us know which one you choose.