A lot of whether you should choose Elemental, Dragonscale, or Tribal leatherworking depends on whether you're using your trade to:
A) Outfit yourself
B) Outfit Guildmembers/Friends
or
C) Make money
Of the above three, A is an obvious answer here. A Rogue wants Elemental Leatherworked armor more than Tribal or Dragonscale. Tribal is mostly geared towards Druids and Shamans, and Dragonscale makes Mail, for the most part.
But..... it can also be very expensive to try and acquire materials for these patterns. Elemental requires... well, Elemental essences and Hearts and Cores. Some of which can only be found/farmed in Molten Core.
Dragonscale is also very expensive to farm for materials, as it requires, yes, Dragon's scales. Not the easiest to acquire, what with you having to kill Dragons and/or Dragonkin to acquire these, in addition to the obscenely high skinning levels required for most of these skinning-jobs.
Tribal, while not the easiest to farm for or purchase off the Auction House, is rather much cheaper on the pocketbook than the above two, and cheaper on time required. The penultimate patterns for Tribal are the Devilsaur patterns, which require, yes, Devilsaur Leather. Devilsaur's are level 50+ elite beasties only found in Un'Goro Crater, and are of a foul temperament. Not the easiest thing to tackle and skin.
In the long run, it comes down to what above will suit your goals for your Leatherworking the best.
Tribal Leatherworking, while geared towards Druids and Shamans, can be worn by any Leather-clad class, with the exceptions of the rare few Druid-specific patterns. The stat-buffs vary, but tend to be beneficial to any of the leather-wearing classes. Unfortunately, Tribal Leatherworking has very few patterns that produce gear that is viable in End-Game instances. Among those are
Corehound Boots(Fire Resist for Molten Core and Blackwing Lair, as well as excellent stat buffs for feral Druids),
Frostsaber Tunic(Frost and Shadow Resist, just what the doctor ordered for a trip to Naxx),
Hide of the Wild(For it's Healing Spells buff), and
Corehound Belt(For it's Healing Spells buff).
Dragonscale Leatherworking, is awesome for Paladin's who are not partial to Plate, and of course, 40+ Hunters and those Mail-wearing Shamans. Sadly, this leaves the most common Leather-wearers, Rogues, completely out of luck. Dragonscale is also a Money-maker, IF you can pick up the rare drop patterns and the hard to acquire Dragonscales. Unfortunately, like Tribal Leatherworking, this advanced form of Leatherworking is limited in it's end-game viability, gear wise.
Chromatic Cloak being one of the very few useful items, since it is Fire Resistant(Molten Core, Black Wing Lair) and Shadow Resistant(Black Wing Lair, Onyxia). Like the Chromatic Cloak, also useful is the
Chromatic Gauntlets for the same reason.
Elemental Leatherworking, the basis of this topic. I myself, Akikokittel on Mannaroth server(Alliance), am a 300-skilled Elemental Leatherworker. So I know something about it. Unlike the other two, this path will suit all leather-wearing classes, but not specifically like Dragonscale does to Hunters and Shamans, and Tribal does to Druids. It's a more general class of Advanced Leatherworking, overall.
Elemental Leatherworking, because it is ELEMENTAL, which includes Fire, Frost, and Shadow, is more suited to End Game than the above two Advanced Leatherworking paths(which is why I chose it). There are varying levels of Fire Resistance(which makes it ideal for individuals and guilds preparing for Molten Core and Blackwing Lair), which range from
Volcanic Leggings and it's counterparts
Volcanic Breastplate and
Volcanic Shoulders to the more difficult to acquire patterns for:
Molten Helm,
Molten Belt, and
Chromatic Cloak.
While I am unsure how/where the pattern for Chromatic Cloak drop, I do know that the Molten patterns, along with a couple other Fire-resistant patterns, are purchased from a Dwarf in the Tavern in Blackrock Depths. This, in addition to the high-level requirement of BRD, requires you to be Honored or Exalted, depending on the specific pattern, with the Thorium Brotherhood.
I hope this helps you in your quest for Advanced Leatherworking.