I have a Les Tam that replaced an old, nondescript GI sling. It's great and will surely outlast me like the GI sling did my dad. I do like the smell of saddle leather.
I liked the utility of the Biothane sling that I tried later and would have gone with that, given the choice (because I'm cheap). The Biothane is not an inferior sling; if you are starting out, I would recommend it over a leather sling. Both require a break-in period. The biothane break-in might take a little longer but I think it will last you through your High Power carrier and that of your children's.
Some people don't like the smell of farm animals or leather or gun powder or diesel fuel. Give it a sniff and make up your mind.