Glass carrier for me (in most cases). For whatever reason, the amount of dust that I have to deal with seems the same with or without the glass. However, I do do a lot of lith printing, which means extended times under the enlarger (2-5 minutes usually) -- my negs, usually 6x6, used to pop until I got the glass carrier. And as Matt has indicated, a larger sized carrier can be masked off to print unusual sizes like panoramas or ditychs, or allow me to print the rebate, without the need to file away any carriers.