I've worked both the commercial and corporate sides of this business. Long term employment is really pot-luck chance. There are plenty of folks who've worked for the same airline for their whole career. Then there's others that have jumped from a dozen or so.
Longevity is really based on the company's financials. On the corporate side, the Coke's, Dow's, Exxon's and any other multinational's have been around for a long time. Executives really like their aircraft, so the aviation department is usually one of the last to go if business turns sour. At the same time though, if you take care of a rich family's aircraft and Daddy dies..... so does your job.
There are numerous types of corporate aircraft. Some are a major pain-in-the-ass to work on. Some not so bad. Given the opportunity to work on Gulfstreams, Falcons, or the larger Cessnas... I'd take that over Hawkers, Lears, and King-Air's. You can't be picky though, a job is a job.
On the commercial side. Company financials rule also. Yes, American, Delta, and United were everyone's dream job up until this plandemic..... now nothing is for certain. Cargo is still going strong. Limited flight benefits on the cargo side vs the airlines. Then you have to decide on if you want to be union or not. FedEx isn't, UPS is. Some extra BS to put up with on the union side, but there are pluses to them also. UPS is highest paid in the industry.
I did Continental for 4 after the Air Force, Conoco for 5 years on the corporate side, and FedEx for 20 after that. I can do both sides (never done piston-poppers), but I prefer the big boys. Being a freighter dog does keep you away from shitters, seats, and passenger convenience items.
Whatever you do..... make yourself valuable. Avionics/Electrical and composites are hot items. Being a damn good well rounded mechanic who understands systems and can troubleshoot them is "always" a winner.