I think sound wise, they are all going to be pretty much the same. Looking at their website the different part are for different "grades" of kits, the cheapest being the installer series. It's the base kit made out of aluminized steel with u-bolt style clamps. The next one is also an installer series, but costs a little more because it comes with a tip. Then the XP series is the full stainless version with band clamps.
I have the XP on my Suburban and love it. It replaced a Flowmaster super 44 welded in the stock pipe. That thing was awful. The MBRP has a nice burble to it at idle and pretty aggressive when you stand on it. I was kind of surprised once. I was following my wife once while she was driving it, and she got in it a little pulling out into traffic, I had never noticed how loud it could get because inside you don't notice it. Best of all, no drone. My kids can watch videos on road trips and not complain about how loud it is.
