Powder coating is not an issue... UNLESS, you have a solid magnesium rim... Truth be told I do not know anyone who has wanted to powder cost something that potencially cost them in excess of 5k a rim.
It all comes down to the type on finish you want... If you want a stock look (Just a different colour) then painting is the best way to go... If your not too fussy, then powder coating is the way to go... Just make sure you get a gloss finish - Which presents more like a satin finish.