Lumineon. People act like it's "forgettable" all the time when I've always been fond of it. I don't think it's THAT generic looking, tbh. So, I've never been sure why it's so "forgotten" or whatever.
I adore Lumineon, especially its cry!
I agree with Galvantula and Mienshao too!
My pick would be Venomoth. It benefitted so much from the physical and special move split because bug and poison types were originally based on the attack stat. Also, Tinted Lens improves its overall power. It's a shame it was rather weak in the generation it was introduced in. I love Venomoth to the point I chained 6 shiny ones back in DPPt.