It used to be Compass (RIP) and Skywest were the regionals with bases there. Now just Skywest but not idea on how senior it is. For majors - last I knew 'pre-covid' it seemed like both was able to relatively get LAX as a base quickly (AA, UA and SWA is my gauge for FO) It all depends on needs, seniority etc. Anywhere you might wind up, you might take awhile to get from their junior base back to LAX. Then at upgrade time it will change all again. It's nearly impossible to 'plan' so be ready for commuting at various times in your career. Too many variables and right now with no one hiring, no one 'knows' . All this said LA is not a bad place to be out of unless you are having to commute to the east coast.