Why Tungsten? It is a weight, simple job....sink to the bottom. Not being a smarty pants here, I really don't understand the value or the extra costs.
you obviously haven't used them...
Smaller profile, tends to get more bites
Harder material, transfers vibrations up your line better increasing sensitivity.
With harder comes slicker... slicker plus smaller weight means the weight slips through the fish's lips easier so you don't have the use you sometimes have of a fish biting down on a led sinker and dramatically reducing the power of transferred in your hook set.
I'm not a "tree huger" I don't do it to keep lead out of the lake (I use lead c-rig and dropshot weights) I do it because you catch more fish using them.
If your worried about fraying look up tackle tour, the tackle doctor (Aaron martens) and look at how he puts inserts in them. I have started...
As for best place to buy... Anglers pro hands down