The main reasons I chose engy on all my toons:

1. The goggles - great stats for shams, and increased stealth detection. Plus gas clouds show up on the minimap when equipped.
2. Hand mounted rocket launcher - not great individually, but significant x 5. Gives shams one more instant attack (we only have shocks other than this), have a 45 yard range as well, so good for shooting down runners. Look awesome as they snake towards the target like a sidewinder missile.
3. Parachute cloak enchant - handy for areas like Icecrown and Storm Peaks where you spend a lot of time flying, and a dismount will equal a death. Combine with hand mounted rocket launchers and shocks for mid-air sniping.
4. Goblin Sapper Charge / Saronite bombs - for damaging vehicles in wintergrasp. Saronite bombs also have a 2 sec cast, which coinsides with the time it takes for fire nova totems to explode = nice AOE burst damage.
5. 5 x Mechano hogs = win.

Cheers.
S.