Depends what you're going for...
If you want something automatic, like a nice rifle, ESPECIALLY able to go full-auto, go with electric. If you had an auto that relied on gas, you would go through a lot of gas, but it would look awesome. There are some out there, but I doubt you'd be able to get your hands on them.
If you want a pistol, go Gas Blow Back.. From what I know about EBBs(Electric Blow Backs), they are complete crap and are inferior to GBBs.