Electric/Dragon and Electric/Bug are the frontrunners right now, but water beats both of them in versitility. Why?
Electric/Dragon offers great neutral coverage. Dragon in general has excellent neutral coverge by itself. But water is superior. Electric/Water hits more SE and, with Ice Beam (which all waters get) it is unresisted outside of Shedinja. Electric/Dragon still has to deal with Magnezone walling it.
Bug has good SE coverage. It can kill off annoying things like Celebi that plague electric types. But water is superior. Water can take out things with ease that electric can't even hit. Water also keeps Heatran out, who can come in on both STAB Dragon and Bug.
OU's Water is Super Effective against that Electric isn't
Infernape
Heatran
Hippowdon
Mamoswine
Gliscor
Rhyperior
Donphan
Dugtrio
Fidgit
Tyranitar
Of those, Dugtrio and Donphan are fairly irrevlevent, due to their rarity, and in Dugtrio's case, fraility. However, Heatran, Infernape and T-tar are HUGE! They are all in the top ten. As I previously stated, Ice Beam can be auto-included as this is a Water type. Water/Electric/Ice hits seven types SE, including Dragon, Ground, Water, and Flying.
Also... water is neutral to SR!!! No problem there!
Electric/Water is weak to Ground and Grass. Thats it. 2 Weakness, and Grass is fairly uncommon. People say that Breloom and Celebi are so common. Well Salmence, who hits Electric/Dragon SE with Outrage and Draco Meteor is number 2 most used in March on SU. Sixteen THOUSAND six hundred ninty-one more Mences were used than Celebi and Breloom combined! 16,000! Don't bother me with Breloom and Celebi!
Electric/Bug and Electric/Dragon are both versitle. They could go both offensive or defensive. But Electric/Water is STILL superior. Offensively, it provides more SE Coverage than Dragon and equivalent to that of Bug. But SE hits on Dark and Psychic are much less impressive as Ground and Fire. It has less weakness than Dragon, and equal to bug. But Fire and Rock weakness can be crippling. While Ground may be bad, the water type shuts down most STAB users, and Grass isn't that great to begin with. Water/Electric/Ice hits EVERYTHING... minus an irrelevant Sheddy, but a common Magnezone and a rare (but more common than Sheddy) Steelix shut down the other combos. Electric/Bug is shut down by Gliscor as well.
In conclusion, Electric/Dragon and Electic/Bug are good types. In fact, the would be my next 2 choices after water. But water takes the good things from both of them, and adds some goodness of its own. Water is clearly the way to go.