Gloss for sure, matte is...well it's matte, not gunna have that deep and shiny gloss in the sunlight. I don't even think BMWP makes a matte finish spoiler, so i'd def. go with gloss on the diffuser to match.
E88 N54 Alpinweiss/Coral Red/Motiv HTA 3586r Tial .82AR/Other stuff...652WHP
F30 N55 XDrive EBII