Well, it depends on what the rest of your team looks like. If you evolve Eelektrik to an Eelektross, you have yourself a pokemon without a weakness (with it having levitation), but it's slow. Super slow. Yet it has a good variety of moves to choose from to tackle a lot of weaknesses.
As for Galvantula, total opposite. Speed is it's game. Having it have Unnerve also has the chance of screwing up your opponent's plans, not letting them eat their berries. Yet you'll often find people use Compound Eyes instead for the accuracy boost.
So really it depends on if you want a slow electric pokemon with no weaknesses or bug moves to learn except U-turn, yet a big variety of other moves to use, or a super fast electric pokemon with low defenses who can STAB with good bug type moves and Thunder. What do you think your team needs more?
"Cogito, ergo es eggo." A.K.A. "I think, therefore you are a waffle."