[EdInk]

Leather or Plastic? (In pleasant grocery store bag boy voice.)

Those are the two choices I consider to be the best too. Leather will "form" to your body better and be more comfortable. Kydex allows a quicker draw and is more durable. Both work very well and as others have said it comes down to preference.

A third popular material is nylon. I would pick it last because of durability. However, it is very comfortable and lightweight. IMHO it is best suited for things like ankle holsters. (Depending on the style, you can sometimes melt loose strings or smooth wear spots with a lighter like you do on a web belt, sneaker shoelace tips or adjustable backpack straps.) Bianchi (and some others) make some "rigid" nylon OWB holsters that fit specific firearms that seem pretty well made.

FWIW I prefer an OWB holster. Not as easily concealed but much more comfortable. Plus, you don't have much/any skin contact with the actual holster. Which means you don't have to worry as much about sweat and oil from your skin ruining the holster.