Hello, I have flown all 3.
The k2 sport has 5pt lle and different colours near the standoffs. It's a bit stiffer but other than that I can't tell any difference between this and the std kite. To my mind the k2 is much more like a slightly bigger nse. It is a big kite and I don't like it in higher winds as it won't trick easily and pulls like a train. It is beautifully built and uses some nice materials. I think I still prefer my nse to fly though. I actiually prefer the opera to the K2 as it feels a lot more freestyle oriented.
The TNT std comp is a cracker. It does everything you can throw at it and if you are a trick flyer it is very good. The LE is 3pt (as is the Black pearl comp) but it will still fly up to 20 mph if you are a half decent pilot. It also has a very familiar feel.
The Black pearl comes with a few different frame choices. The comp is is the best and it flies similar to the TNT and almost as good. It is somewhat cheaper than either of the others.
Both comp versions of the TNT and the BP fly almost down to UL territory and have a huge usable wind range.
If it was my choice I'd have the TNT comp first then the BP comp second with the K2 third but hey I'm a trick flyer. I hope this helps