Eyeball tattoos are a gimmick, the risk of permanent damage to your eyesight is not worth the aesthetic IMO. Get some cheap coloured contacts if you want the hallowe'en-psycho look ...
Blackout tattoos are great if you want that specific look and/or want a fresh start over some old ink. I've seen (healed) white over blackout work quite well, but I've also seen examples where the white doesn't quite pop (ie dependent on tattooists skill and how much scarring from covered tattoos below). To each their own, I am starting to enjoy abstract tattoos but the "brutal-blackout" look is a bit crude to me. Creatively I think there are more interesting ways to approach layers, blastovers and coverups...but hey express yourself however you choose. cheers