Nothing compares to Snickers ice cream bars... except Magnum Caramel & Nuts
The Twix ice cream sux, there's no other way around it...
As for actual candy bars...
It's a tough choice between Snickers, Twix, Kit Kat, Kexchoklad (Ok, maybe not a bar) and SPORT Lunch. I've grown pretty tired of Snickers, and (despite it's magical taste) Twix can be bothersome and dry if you eat more than one... Kit Kat is very good... but the bar really isn't the best format to enjoy it.
So... in short... all I know for sure is that Mars and Milky Way really don't even come close.