Salmonmac's link is a good thread to peruse when looking at buying interchangeables. We all have our druthers when it comes to needles.I've never used Addi's, but I hear they're great. I'm a firm believer in the old saying 'measure twice, cut once.' To that end, I loved Knit Picks Try-It set, 3 sets of common size tips, one wood, one metal, one plastic - all interchangeable, cable set included. An inexpensive way to begin to figure out what you want to spend your money on, at least where tips are concerned.
As with all things, your mileage may vary... enjoy the search.