I would start by saying get a more reputable brand of wheel like HRE, Volk, Advan, BBS... Secondly I would say that it's true that both of those sizes would work but it's hard to give sizing advice without the wheel width and offset.
'04 E46 M3 - Jet Black - Sold
'08 E90 M3 - Alpine White - Sold
'13 E92 M3 - Silverstone II - Sold
'13 E92 M3 - Alpine White - Ohlins TTX, Fall-Line Suspension Arms/Bushings, AP Racing BBK, OE GTS Aero, Cobra Seats, Akrapovic GT4, GMG 4-point, BBS E88