I chose Gnomish, and I really wish I would have went the other direction. Being able to reload Mortars and Use Bomb Dispenser I believe is more important than the battle chicken and the deathray. Battle Chicken is obsolete by level 50, and the death ray does so much damage to you to use, that Im not sure its really worth it in most cases.
The things I have found to be the most useful..
1. Goblin Rocket Helmet (Helps with Crowd Control in instances) and since Im a Shaman, I normally can't help in that dept. It has a 20 min cool down, but in instances, that can sometimes get you to the next big 4 mob pull challenge.
2. Gnomish Shrink Ray Ok, this isn't REAL useful, but it definatly has some funny affects, and 2 out of 3 times, you get favorable affects from it. Either increasing your partys size and attack power, or shrinking the enemy. I don't use it when I feel we are on the edge of survival, but when I know we will win regardless, its always a fun item to use.
3. Gnomish Mind Control Helm. This works ok sometimes, its more of a pvp item then anything else. If I am going to attack a group of 2 or 3, I will throw this on and attempt to Mind Control the rogue or pally or warrior. And immediatly sick em on their friends. Sometimes it works, other times it doesn't, but when it does, its pretty funny watching the enemy freak out.
4. Gnomish Harm Prevention Belt. I will put this on sometimes in pvp.. It has saved me numerous times, because either it saves me from 800 pts of damage, or I get banished for 10-30 secs.. which many times the enemy moves along to fight someone else by then.
All of these useful things can be used by both, just takes finding a gnomish eng to make some of them. I would suggest that you go Goblin, and trade some of your items that would be useful to the gnomish engy, for some of the items that would help you out.
In the end.. Bombs > cool devices with long cool downs. Battle chicken is ok, I use it more when I am mining and I get something interupting me.. I pop the chicken and finish mining before I start fighting. Keeps some of the guys who like to let others aggro the mobs guarding the vein and slip in behind it away from ya