Consensus seems to be that banggai cardinals are the easiest as their fry come out fully formed. Then there are clowns and a few others possibly that lay eggs and go through a larval stage that require a bit more work but are still not too difficult.
Things that can affect your decision are do you want to try and sell them or just do it casually, which effects how big of a setup you need (just a pair or several), do you want to try and get into breeding different specific patterns or just propagate the species (Banggais are pretty much set in form, while clowns can have a huge variety of patterns and colors). Also have to consider your location and what is in demand there (some places you can unload all your young to lfs, others you may have to look harder or ship them in order to sell them all).