I was in the same boat so I'll give you a detailed brain dump..
I had CR Lab's the last two seasons but I needed to replace this year cuz they were beat to shit from moguls and park at Killy. I was originally just going to get another pair of CR's or SPKs.  They (CR) are a really fast ski and once you get used to the mounting, they carve really well and tear up trees and bumps.  However, I went with Karmas to replace them.  Not really because I think they were that much better, but because I wanted to try something new and I heard the Karma's are a better all mountain ski.  I'm also a bigger (6-1, 200) and even though the CR's held up exceptionally well, I wanted more of a landing platform in the park and in general.
If you really are more focused on park, get a pair of CR's or Candide's on evogear for 399.  They are a much better ski than the SPK and a lot cheaper.  They are stiffer and have the best base of any twin out there.  The one warning I have about the CR's/SPKs is that they suck in powder.  I did a cliff drop under Harmony chair at Whistler in 05, the tips immediately dove, and I tomahocked all the way down the mountain to the amusement of all on lift.