gnomish or goblin engi for pvp?

[Mryul]

what's best for a healer?

and in general?

[Datruth]

Doesn't really matter, since they can use each others gadgets anyways (the relevant ones at least).
That being said, if you do PvE aswell I would say Gnomish, because the gadgetzan teleporter trinket is gonna come in handy once AQ comes out.

[Mryul]

are there no exclusive items?

[Thunderstruck]

Most of the goblin/gnomish stuff I'd consider using in pvp is tradeable and usable by both such as bombs, Gnomish Rocket Boots, Gnomish Mind Control Cap, Gnomish-Net-O-Matic Projector, Gnomish Shrink Ray, Goblin Rocket Helmet and Goblin Morter.

So, let's look at what you aren't able to trade:

Gnomish: Gnomish Death Ray, Gnomish Battle Chicken, Little Smokey pet, Gnomish Alarm-O-Bot, World Enlarger,
Goblin: Pet Bombling, Goblin Dragon Gun, Goblin Bomb Dispenser

So really it's more personal preference. I have a Gnomish and a Goblin engineer so I can make everything and trade.

[Niko]

Gnomish.

[Avise]

Gnomish.

Gnomish: World Enlarger

[Colezz]

rogue + nogginfogger small buff + world enlarger + stealth = easy flag caps