I'm in the same boat! I just bought the gold vintage alhambra necklace - one motif - in MOP. I plan to get the matching 5 motif bracelet soon after. I think it largely depends on your skin/hair coloring and what you wear often. I typically would be all about the all-gold style; however, I think the contrast between a color (onyx or MOP) and the gold chain is stunning. I went with MOP (despite living in black clothing and accessories - ha) because i think it's just stunning and will go with literally everything (and is seasonless). As I build my collection, onyx will likely be my next choice. I have blonde hair, blue eyes, lighter skin tone as an FYI.
Let us know what you decide!