Ok, I don't have an M3 yet, but since I've started the ordering process, researched color and trim choices like crazy and my head literally *hurts* from trying to decide on color combinations, I thought I'd add my two cents, lol.
First, you can't buy the OEM piano black trim from BMW unless your car has a VIN that confirms it's Individual.... So unless you're planning to go aftermarket, if you want the real piano black, you need to have an Individual car.
I think trim depends a lot on the overall color combination. And if you're trying to go for classy or sporty.... or both (although both can be tricky to execute well, IMO). So I have a few different options in my head, depending on what I ultimately pick inside and out, and am looking forward to hearing other people's responses....
2013 M3 coupe (Azurite Black, Black, Piano Black)
+ miata nut (2 miatas) + Mk6 GTI 5-door hatch (our mini-SUV