What is the difference between the blood trails using a 2 blade cut on contact style head like the magnus 2 blade vs a 3 blade like muzzy or thunderheads?

It all depends. If both arrows pass through at the same spot than the 3 blade with a larger cutting diameter will leave a better blood trail due to the larger exit hole. However, two blade broad heads have a better penetration so in theory if a two blade passes through where a three blade might not have then the two blade would leave a better trail due to the exit hole. All in all I doubt there is a noticable difference although I prefer the three blade.

http://www.broadheadtests.com/FAQ.html

There's a little difference, but not much with a low exit. If you use a 2 blade a smaller diameter arrow will help with penitration.