I want to say the Bianca, but they honestly crush my toes after a while.
I'd say the most comfy style for me is a tie between the New Simple and the Very Prive.
The Louboutin comfort thread has a ton of information in it, you might want to take a look. A lot of members have actually rated styles on a scale of 1-5 (I believe) in terms of comfort. Super worth a peek!!