Depends. Life Orb Electivire would be unstoppable if it's motor drive boosted it's speed a stage. But if you want bulk, AV Electivire is the way to go. Here are movesets for each:
[email protected] Orb
Trait: Motor Drive
EVs: 252 Atk, 252 Spe, 4 Hp
The AV set is basically the same one above except it's holding the AV instead of Life Orb. Hope I helped!