I'm (still) in the process of selecting a small/medium milling machine and I can't decide between an R-8 spindle or a MT4 spindle. This is in part because of two reasons, firstly I don't really know too much about either or the advantages/disadvantages of either and the other reason is because I can choose either way at this stage because I can only see myself using an ER32 collet set with most of the tools. As such an ER32 to MT4 or ER32 to R-8 are equally available so no real consequence.
I have picked other peoples brains and naturally the sellers of a machine with R-8 will tell you that it's a superior spindle and same same about a seller with an MT4 machine.
The only piece of info that interested me was that R-8 is better because it is less likely to bind up compared to a MT. Was told that a MT can heat up and may require a hefty wack with a hammer on the draw bar to loosen if it is on too tight....
Someone throw me a freakin bone here!