KWA MAC 11, or the KSC TMP, but those are both gas rifles. If you really want something unique, I would suggest Tokyo Marui's Scorpion, never heard a thing about them, but it certainly looks amazing.
Still, theres alot to be said for the MP5 series, considering how many good versions there are today. As for the P90, just buy an Echo and drop a lower spring in there to get a CQB allowed speed. Works like a charm.