Best method of removing old gaskets?

Three choises

Gasket scraper. Looks like a chisel, is much harder to damage the aluminum underneath compared to using a razor blade.

Gasket stripping wheel. Goes on the end of an air tool, has a few dozen hard rubber fingers that eat through any gasket material, but will not damage aluminum (the rubber tears up first). I love these things for big jobs, they work awesome. Get at any auto parts store.

Chemical gasket remover. I've personally never tried em. The thing above works so well and so fast that I never seen a reason to make a mess.

I try not to use anything harder that the material I am trying to remove the gasket from. So I don't use a steel scraper on aluminum but hard plastic scrapers or even and oil credit card work well when combined with some spray remover. I'vae also used a Scotchbrite pad system that is very good that tou can either chuck in an air powered die grinder or electric drill.

I use aerosol gasket remover and a hard plastic scraper. It works very well, and won't bite into the aluminum. Then I clean the area thoroughly with contact cleaner.

In a pinch, paint remover does an excellent job. I like it because you can brush it on vs spraying everywhere.