SO, yeah, I was going to blindly and immediately post SPC700, which I really do love. Fantastic music out of that one. But the SID was fantastic as well. Love me some Last Ninja!
I don't really have a favorite. I think this quickly turns into a Megadrive VS SNES topic, as after these consoles CD-Audio became much more prevalent. I respect and love both the Megadrive's and SNES' sound, composers who knew how to tame the chips created some particularly timeless and impressive soundtracks. As far as computers go, I'm not a huge fan of OPL2/OPL3 stuff, despite the fact that I grew up with these. In all honesty, I consider them underused, Dune, for example, did wonders with these chips. SID music is always awesome as well . https://www.youtube.com/watch?v=MYTDGqYmvZw
Konami VRC7 is pretty interesting. FM synthesis for Famicom that sounds very similar to Megadrive: Particularly into 43:09. Sounds exactly like an impossible last boss in a Konami game should sound. Also 24:52, 32:42, and 38:18. This game has a pretty kickin' soundtrack man.
The VRC7 contains a full Yamaha YM2413 on silicon which gives the NES to do 6 FM sound channels. I think its the same sound chip as Japanese Master System's. Its a tiny little sucker too.
I wish I could play Lagrange Point on original hardware without buying a Famicom I've heard the music, it's remarkably good.