The grind is really bad at the thick and rugged leather spectrum of things. Knothide, Borean and even savage leather were nowhere near as bad.
For Thick leather, I killed mobs in the Badlands. Nyxondra's broodlings. They have an very fast respawn rate and there are often people there farming for the rare pet.
I ran instances (UBRS, Dire Maul) and even AQ20 for rugged leather. The truth is, the best place to farm for rugged leather is Dire Maul north. Kill the first two rooms, loot and skin the 30-40 dogs in both areas, reset and restart. (mind your lockout)
Knothide leather, I ran Karazhan. The servants quarters immediately to the right of the door, there are bats and dogs to kill. As long as you do not kill a boss, you can reset the trashmobs in this area and farm all you want. (minding the lockout)
Borean Leather, you can run Gundrak and skin the place over and over, run Violet Hold over and over or you can kill the raptors around Gundrak. While there's only 12 - 14 of them up at a time, they consistently drop 3 borean leather at a time and I actually found this to be the fastest for me.
At 400, you can use any fur lining enchant to get you to 425 - 435, which GREATLY alleviates the struggle with getting to Cataclysm level LW.
Savage leather, the Molten Front or Tol Barad have the best farming areas. For the molten front it's cinderweb spiders. In Tol Barad you can skin the crocolisks or the spiders. If you don't want to open up the Molten Front dailies, you can just use the port to Tol Barad and farm there.