I stick to Quaternion also, its what Biped was originally built on and what it seems to function best with. I run into a lot of problem when its set to Euler. Things like tangents resetting to default when saving/loading animation, what good are bezier handles if they reset? I leave "separate tracks" at the default…
Most animators prefer working with Eueler because you can see and directly edit the f-curves. However, if a rig is careful with setting rotation order you can avoid most issues with gimbel in most circumstances. It's impossible to avoid in all situations, but you're really only going to run into it in the ball-and-socket…
I've used all three and I have to say that all three, save for the 2.5 version of Z-brush. All have their advantages, but to be honest for the majority of what you really need to do Silo 2 is more than sufficent. I've been pushing between 2.5-3 million polys in it, so breaking the mesh up into pieces I can double digit…