Provia's great. Some people say it ain't saturated, you just have to know how to use it ;-).
Velvia, IMO, is great for certain subjects only. Personally, I'm more of a "represent it as it really is" kinda guy, at least 90% of the time. The other 10%, I like to go hog-wild, so I use Velvia 50 .
Astia is great too, great for skintones, especially in the studio, where you can control your contrast and lighting easier than in the field.
Negs are for people who don't know how to properly meter their shots . Just kiddin, I still shoot Portra, sometimes...