1/4th and .093 kydex for me. The thicker kydex just seems to mold better, "stays put" in the press, and it doesn't transfer a hair or a piece of lint, or a microscopic amoeba into an eyesore in the finished product. I ruined a whole big sheet of .060 kydex because of these problems. Maybe I'm just not good at it...lol.
I use the dies from Tracy's. Expensive, but I've never had a problem with any eyelet cracking or anything. Get the 1/4th set, and some of the premium Siska eyelets. They don't have any issues flaking, or anything, like others have reported. They stay black and wear really well.
I use my cheap harbor freight drill press as a kydex eyelet press, and it works great.
Btw, if you're interested in another one of my methods of madness. I never really grind on my kydex too much. I see these guys on youtube grinding a whole huge sheet into the finished shape. That can't be good for your lungs, and is definitely one giant ass mess. I draw my finished shape around the mold with a lead pencil, and score it with a utility knife. I then use my Leatherman to just break the pieces off. Score the drawn line, break. Score against the broken edge on the backside, break. It's pretty easy to then take it to the grinder and finish it. Minimal dust.