this is wot i know not opinions but facts:

magnex is the best fitting exhaust will not rattle or anything and is the only one to have a flexi which will dampen the vibration, only downpoint to this system is its not as loud as the others
Scorpion sounds good but is the most restrictive so not very good performance wise, no flexi so not as good fitting as the magnex
Mongoose is the best for performance and sounds the best too, once again not as good fitting as the magnex.

The problem with the systems without the flexis is that if you have an engine which cant stay still the vibrations go to the exhaust and can possibly snap off your bolts doesnt happen all the time but can happen, way to get round this is to fit a flexi!!!!