Gnome Eng. VS Goblin Eng.Follow

They are more or less the same. Gnomish engineering is mainly focused on "fun" devices such as Mind Control Cap while Goblin engineering is more about explosives. As a Goblin engineer, you will be able to make a lot of explosive that will aid you in PvP battles. Goblin/Gnomish engineers can use products created by each other except "Gnomish Death Ray" which is BOP. Everything else is BOE I believe.

Level 300 engineer here (just got 300 tonight by making an order of thorium widgets for a customer to hand in in the darkmoon faire) and i would say that gnome engineering would probably be the most useful PvP AND world useable version. Gnomish engineering you get the mind control cap, great in PvP especially against 2 high level horde :P Now, the great thing with the cap is, when mining rich thorium veins in high level areas like winterspring (im only 52) and there is an annoyingly high level humanoid mob standing beside your vein? simple, pop out the cap, mind control the target, and mine the vein. The 20 seconds gives you just enough time to grab 4 swipes, the maximum a deposit/vein can have. The same works with the net-o-matic, just lure the mob away from the vein, net it, and go mine your treasure :)