Leather all the way.
I just got two really nice rolled leather collars from Master's Pride. They still look brand new after a full week of hard wear, including playing in the ditch, etc. I'm impressed so far! I love how they look too, so simple and obviously easier on their fur.
Also just got an EL braided leather lead. Its not my first leather lead, but its my first made from that delicious black latigo I also have collars made from. Words cannot express how I'm loving this leash! Well worth the price.
I've had other leather, mostly EL except for an overpriced police lead I was given. I freaking loved that lead, but no way in hell was I going to pay to replace a $90 lead. Not when I can eventually get an EL one for $50 and get it customized to boot if I need.
For harness I have a Stillwater leather walking harness. Use it for agitation. Its perfect. I've tried other agitation harnesses and none fit the girls as well as this one. THe leather is very nice, but the 1st time I cleaned/conditioned it, it did bleed a bit. Its my second one... Scout ate the first one that was burgundy and so I got black this time. Can't beat the price either!
I bought a 1.5" leather Stillwater collar at one point... I ended up giving it to my friend who has a big ass dog because it was way too much collar for Lily. She pops it off and on his head without undoing it, lol.
I like biothane too. I just have leashes in it though.