I've been using this particular tool for about 14 years now. I find it has the least amount of chatter, easy to grip and use and the big one is that it's edges won't dig into a fretboard if you slip off the fret. I've bought other ones from Stewmac to try em out, but I keep going back to this one. A buddy of mine decided repair work wasn't for him and sold me his two so now I have 3.
Dual-grit Diamond Fret File | stewmac.com