Maybe it's because I'm already fucking excited for Rashid, but that theme's already shaping up to be my new favorite. However, I don't want to make that judgment already, because the small snippet of F.A.N.G.'s theme we have is pretty rad. I love how it starts with Muzak before picking up... Into a similarly chill tune. It's weird, it's not conducive to fighting, and definitely doesn't sound like a boss character's song, but it's F.A.N.G.; everything we know about him seems to point to this fitting him like a glove. So until I hear his entire theme, I don't know if I can call Rashid's the best yet.
... And then there's the fact that we have remixes of Guile's Theme & Jazzy NYC coming.