This is a really difficult question. There are a number of contenders here... CPS 2000, SS 300, SS 100 mk2, XP Pool Pumper Blaster, Aquapak Devastator, SC 600, the XP 150 of course... I have fond memories of the Lightning, and contrary to a lot of people here I actually really do like the Monster XL. I guess if I really had to pick it would be the CPS 2000. It's hard to go wrong with <arnold voice>So much powahh!!!!!</arnold voice>
I should probably get another XP 150 and get reaquainted. I always heavily mod my guns, and over the past few years I've been using other guns in that size category, especially the SC 600 and SS 100 mk2. My modded 600 gets about 40 feet, so it's hard to argue with that. I really like the way that the XP 110 and SS 100 handle, moreso than the 150, but again, that may just be because I don't use it enough. The 110 is, however, arguably the most maneuverable/easy to handle blaster overall and I have some modding ideas, but it doesn't have the quick trigger, large PCs, or large pump of the 150. I have a feeling that I'll probably end up using a lot of lighter backpack weapons in that size class ultimately. The PPBs are kind of like 150s but with more PC capacity and a slightly less quick trigger. The PPB would probably my 2nd favorite then. Of course, this all depends on welding the 2 firing pin/rod things together. I can't wait til that all gets done. Water warriors never run out of projects. That's for sure.