Right now I'd have to say my G1 Kup or Animated Arcee tend to really look out of place to me all the time. Haven't opened my Titanium Roddy or RID Landfill yet to say if they'd fit in less or not.
I got the D-Arts Megaman X awhile ago and still don't have a good place to put him. It's a sea of Transformers, Gundams, and a single human looking robot.