Cover Flow looks cool, but I find it to be quite impractical a lot of the time. Useful for images etc., though.
List view is great when there's loads of items to look through. I hardly ever use column view anymore now that Leopard has the Path Bar feature. It seems to be the standard for file saving dialogues, though.
I LOVE how in Leopard you can change the grid spacing in Icon view, though. Icon is definitely my favourite view.
I only ever use list view. I honestly cannot stand when my Applications folder somehow resets to being in coverflow mode. Gah. Coverflow is cool for a pictures folder but that's about it...
List but I do use coverflow when searching for something. Annoyingly there seems to be a bug where I cant move objects when in list or coverflow. It only happens occasionally after many hours and goes if I feel bothered to restart.