Both the same. They're both black = pain in the ass to keep clean, but looks stunning when washed and waxed. Sapphire Black is a metallic color, so it looks a bit nicer. Jet black is non-metallic, and looks much deeper when clean/waxed. Can't go wrong with either!
Imola Red / Imola Red ///M5
E60 SSK, Dice iPod, Illuminated ZHP knob, GT Custom Exhaust, BCR Coilovers
'01 330Ci Titanium Silver on Coral Red
'96 328i Jet Black on Black