Luxray
Pros
Great 120 Attack Stat and usable 70 Speed.
Decent Ability in Intimidate.
Decent STAB in Thunder Fang and Wild Charge.
Available fairly early being Route 8.
Cons:
Rivalry isn't the best ability, so aim for Intimidate.
Shallow movepool of STAB, Crunch, and Facade.
Ampharos
Pros
115 SpA and good Bulk.
Usable ability in Static.
Good movepool in Thunderbolt, Power Gem, Dragon Pulse, Signal Beam, and Volt Switch.
Cons
Bad 55 Base Speed.
Have to trade it into Sun and Moon.
Conclusion: I would go with Ampharos only, and only if you have the ability to get it in Sun and Moon, via trade with USUM. Otherwise, you are stuck with Luxray. Here are movesets for both.
Luxray@ Magnet
Intimidate Ability (Preferred, but Rivalry can do)
- Thunder Fang
- Wild Charge
- Crunch
- Facade
Ampharos @ Magnet or anything really
Static Ability
-Thunderbolt
-Power Gem
-Dragon Pulse
-Signal Beam/Focus Blast
Again, unless you can trade for Ampharos easily, just use Luxray.