What you want to do is to get Windows 3.0 emulated on your Amiga, then use an old version of Microsoft Paint. You can't go wrong there!

Personally I've been using a mixture of DPaint and PPaint for my sprite editing needs, though I am not too well versed in either program as I project originally began while working on a Windows machine some 11 years ago. None the less I like to try to do as much of the graphical work on the Amiga that I can because of the program's unique ways of dealing with things.
I've always been curious about Brilliance, but never really stuck around to learn much of it. I'll prolly get back to it sooner or later.