I have the Knit Picks Harmony Options (and I love them a lot!) and I've been aquiring the nickel plated tips as I think I need them. However, I handled the Addi Clicks at the LYS yesterday and suddenly I'm tempted to get a set.
If only they weren't so expensive!
Choosing needles really is a personal decision -- I don't think there is an overall BEST set, just what is best for each INDIVIDUAL. There are several excellent and detailed threads that discuss the differences, pros and cons of interchangeable needles -- I read all the ones that I could find before I purchased mine and it helped me make the decision.