A lot of handloaders will tell you that the excellent Vihtavuori N320 is the standard for cleanness to which all others are to be judged. It is a good, clean powder and I use it. I don't care that it cost more as the cost of powder is the least expensive part of my handloads, especially 9mm. Instead of costing 1.1 cent per round it costs 1.8 cents which isn't going to kill my budget.
But I can show you soft shooting and accurate loads that I have worked up with that powder that will foul a spotless clean revolver so bad after 25 rounds that debris under the star will not allow the cylinder to close or buildup in the BC gap that causes the cylinder to drag. It really comes down to a number of factors but especially the actual load you are using. Alliant Bullseye has the opposite reputation, that of being dirty. And yet a lot of shooters use that powder and you cannot talk them out of it.
Personally, and I'm not the standard of all things but I usually clean my handguns after each use. For several reasons. Usually I put several 100 rounds thru them when I do use them, also I want to know that my handguns are in great condition, clean and every screw and pin is in place.
I think every powder has it's application(s). It might not have an application for the individual shooter though. Without any published load data and no forum user imput or experience, although there is some old load data for similar application in some old out of date load manuals, I managed to work up a decent handgun loads using Vectan 206V and AS. Both are clean and accurate. But it took quite a bit of time and trial and error.
Not exactly off topic but sort of relevant to the discussion but there is a huge difference between the burn profile of HS-6 or CFE-Pistol and Bullseye or Titegroup. All of those powders will work in 9mm but some loads will be dirty in some guns and others will be clean using any one of those powders. There are other factors not just powder profile.