Skywest is the only significant non-union airline. At the regional level compensation is determined by market forces, not any particular union actions. Regional unions provide some services for a cost, but it's not really significant either way. Whether you should participate for the general enhancement of the profession is up to you.

Other than regionals, you're better off with a union shop as a pilot... the job does not lend itself well to office politics... if that's your style, there are plenty of bottom tier 121, 135, 91k, 91, etc operations where you can get ahead by shmoozing. But the best you'll ever do, unless you're exceptionally lucky, will be less pay for more work than the union major pilots.