I personally like the sheaths on the RC-3 just for the ease of carrying it so many different ways. When carrying it in town I wear it horizontal strong side underneath a jacket in the cooler months, and vertical between the waistband and belt underneath a t-shirt in the warmer months, both methods using paracord. In the woods, I carry it with either the molle back sheath, or a decent leather sheath I made for it myself. I like the different options to suit my mood.
As far as retention goes, the coyote brown sheath that came with mine was super tight, but loosened up to just what I like it at. I also bought another sheath in foliage green, and that one came perfect and has stayed perfect for my preferences.
As far as my favorite sheath material goes, I prefer leather. I don't love the idea of plastic/kydex rubbing on my edges, but it's more preference than anything, really.
Kyle