I voted Dru, mainly because I think she would fit in more with the other statues. You could have a great scene with a vamped out Spike, Angel and Dru, very reminiscent of season 2 (which is one of my favourite seasons)
Illyria would look awesome and she would fit with the Angel and Spike, but I guess I see this more as a Buffy line, rather than Angel. That also rules out Wes for me as he was a minor character on Buffy really.
I have nil interest in Cordy, Connor, The Beast or Glory and I don't really think The Master or Vamp Willow would fit in.
Darla would work in with the quartet of vamps, but I wouldn't actually want a statue personally.
I'm pretty happy with what we're getting really - Buffy, Willow, Faith, Spike and Angel are probably the most known and loved characters. I'm also happy with my Buffy maquette, if there was another one it would be kinda weird having 2 Buffy's to me.