Personally I love engineering for resto (both PvE and PvP). It take a smarter player to manage (and remember) their engineering cooldowns, but if you can do it then it's more beneficial than some other professions.
You get:
Nitro boots: They can save your butt in case your a little slow to react to something. If used wisely they can also let you get a few more heals off durring movement fights. They also give a static 24 crit rating, *but you give up 7mp5 or 15 stam + minor movement speed form enchants.*
Hyperspeed Accelerators: 340 haste for 12 seconds with 1 min cooldown. In essence, 20% up time if you use them on cooldown. I'm pretty sure that equals 68 haste when balanced out, although I'm terrible at math. (340 * .2 = 68) If your a troll you can get 2+ mini bloodlusts during a fight by macroing these with berserking. *By taking engineering you cant get 28 spell power to gloves enchant.*
Some numbers on Chain Heal with WoA down:
Base gear (1211 Haste) - 36.93% - 1.74 sec cast
*as a base reference* Lust - 1.34 sec cast
Gloves - (1551 Haste) - 47.30% - 1.62 sec cast
Troll Racial - (20% cast speed) - 1.45 sec cast
Troll Racial + Gloves - 1.35 sec cast
Lust + Gloves + Racial - 1.04 sec cast
You can macro the gloves to chain heal to use it every time its up, macro it to racial (if your troll), or just use it when you feel necessary. I macro mine to racial for a very nice haste boost. You can usually get 2+ uses during a fight.
Frag Belt: 750-1k damage + 3 sec stun. Pretty useless in PvE, but it doesn't take up your belt buckle so its free and you can cast it on the move (only practical use would be a FC type fight or if you get aggro on trash)
Springy Arachoweave: +27 sp to cloak and slowfall on use. Again, pretty useless in PvE since most of the time +23 Haste will be better, but it could have some uses for a tank healing set.
Mind Amplify dish: +45 stam and an on use MC (uses helm Glyph spot). Useless in PvE, but fun to use in PvP
The main reason you would choose engineering for PvE is for the gloves (if your terrible with cooldowns, just macro it to Chain Heal and be done with it) and the boots are very nice in situations also. You also get plenty of other useful gadgets like jeeves, wormhole generator, mote extractor, bank, etc... People that say engineering is useless in PvE are misinformed.
But err back to topic... my rating would be form best to worst: 1. JC, 2. Engineering or BS, 3. Alchemy, 4. Tailoring/LW/Enchanting/Inscription.