The best kits are going to have stiffer springs in the accumulators, or shims that go under the springs, but they are going to cost more. When spacers are used in accumulators, the kits are cheaper, but are harder on the "hard parts" in the transmission. Springs cost more money than a little spacer, but a spring gives more "coushion" to the clutches wich will save wear on the hard parts. Just remember that the cheapest are not the best, and the best are not the cheapest.
I was able to re-programm the computer to adjust the shift times for my GTP to get crisper quicker shifts, Personally I would not want them much more than they are now (I'm getting older) LOL. When I was younger, I loved feeling those shifts that was like getting kicked in the pants, but now not so much, just wanted to reduce slippage and heat, and so far it hase been doing good. Hope this helps.