Stainless is much better but costs more.
As for powder triple 7 (777) is by far the cleanest. True BP is cleaner than Pyrodex but there is extra paperwork for it which puts a lot of shooters off. I get my 777 through the post with no special box needed for storage, less hassle that way.
Some clubs insist on BP in competitions especially MLAGB linked ones. They insist on traditionalist shooting and frown on Ruger Old Armies or modern sights.
My own view is the more people we have and can get shooting the better for our pastime. So I like 777 in my old hog leg and dont like restrictions to put people off.
“If a cricketer, for instance, suddenly decided to go into a school and batter a lot of people to death with a cricket bat, which he could do very easily, I mean, are you going to ban cricket bats?” :- Prince Philip said after Dunblane