My favourite villians include the likes of the Turks, Joffrey, Tywin, Vaas and Leonardo DiCaprio's character in Django Unchained. Those kind of characters. Somewhere between crazy and well dressed, smooth bastards. Vaas is probably my all time favourite, even if he doesn't quite fit the latter.

One thing that links these characters along with my other favoured villians (exception to this rule: Sephiroth) is that they can be very funny, generally in quite a sick kind of way. I think FF villians tend to take themselves way too seriously to be amazing, incredible villians. Sure, there was Kefka, but he was a bit too far into the far end of the spectrum with his clown face, psycho laugh, etc. which made him slightly unbelievable, like watching a cartoon. This worked okay for FFVI but I don't think it would work great in FFXV. Although if you take away the makeup and magic, I feel his personality is kind of similar to Joffrey. xD

I wouldn't be against that blonde guy being the main villian in FFXV. The one that is on your side. That'd be a neat twist, and he seems best suited to carry it out and still be pretty cool.