I can't really speak to the 20ga, I just started loading for that last summer and still haven't found anything I "like". Works, yes. Prefer, not yet.
For the 12ga though I don't use anything but International Clays for up to 1-1/8 oz loads. Great powder for speed, my 1oz trap loads chrono about 1275fps. And it's clean burning. I've never liked 700x, although I do have 8 pounds of it floating around from when powder was non-existent. Always too dirty for me.
Remember, shoot straight and shoot often.
Good... Bad... I'm the guy with the gun.