Hi Andy and welcome to the site.
Both the Insane and the AM xxx are great boats. Your decision should be based largely on which one you like best as far as looks since they are pretty close in performance. I can give you a few differences that might help you decide also.
The Insane Gen 3 is a faster hull than the XXX in general, because of it's bottom design. The layup is also thicker and will be a bit more durable. The XXX on the other hand is a boat that will handle "bigger" water better if that is a factor for you. Both can be great heat racers, but I take it that will not be your primary use for the boat. Don't take my comments about the layup as a negative for the AM, I am simply pointing out the fact that they are not laid up the same.
I personally would have a hard time choosing between the 2 if I had to!

I personally race the Insane. I have been doing so since 2004 (running different generations of the hull) and love them!
Another hull to consider if you are looking for a big water boat that can also race is the AC Lazer. The AC Razor also.
For pure racing, there are also the Stryker Y6, and Rampage which are great boats.
The list is long, but what I always tell people is pick one that catches your eye and go with it, while staying with the reputable companies.