I have 2 very close friends one who works at CEC and the other is the importer for Kleemann in the States. They have this HUGE grudge match going between them. Here are my thoughts and this comes from driving and riding in their cars. Both are E55s.
For outright speed and pure physo experience you have to go Kleemann.
For best overall package some cosmetic, some performance, some luxury you have to go with a AMG with Brabus touches.