DraStic

I want to play Pokmon Black 2 and I want to get the best look. Which filter is the best for picture quality? Scale 2x, quilez, hq2x?

There is no real best one. It's a matter of preference. Just go with whatever looks best to you.

Use whichever you think looks best. I personally don't use filters often, but when I do, I go for 2x scale or Quilez and avoid HqX filters. However, I like the games as they were originally, and prefer the pixelated look to the smoothed out/fuzzed look you get from a lot of filters.