pretty minimal difference- unfileds being a bit 'fatter and darker' but it's a very small difference in most case- however, the exception that proves the rule...... duckbilled mouthpieces (Bergs, Jody Jazz DVs, Levelaires etc) seem to prefer unfileds. In my experimenting they play less squeakily and the fatness of tone is, well, fatter (this is a tip from Jody Jazz in relation to his own DV mouthpieces, and- yup- unfiled does seem to complement 'em better)