Boltund
- Yamper can be obtained earlier than Toxel
- Good Ability in Strong Jaw
- Astounding Speed
- Respectable equal attacking stats
- STAB moves super effective against Nessa and a few Pokemon in the Champion's Cup
- Learns moves like Wild Charge, Play Rough, Fire Fang, Crunch, and Psychic Fangs
- Quite frail
Toxtricity
- Good Ability in Punk Rock
- Exceptional Special Attack and respectable Speed
- STAB moves super effective against Nessa, Opal, and a few Pokemon in the Champion's Cup
- Learns moves like Overdrive, Sludge Wave, Boomburst, and Volt Switch
- Toxel is obtained slightly later than Yamper
- Until it evolves, Toxel is garbage
I think they both work fine. Use Toxtricity to hit harder specially, but use Boltund for a fast, hard-hitting physical attacker.
Boltund @ Life Orb / Expert Belt
Ability: Strong Jaw
- Wild Charge / Thunderbolt
- Psychic Fangs
- Crunch
- Fire Fang / Play Rough
Toxtricity @ Wise Glasses / Poison Barb
Ability: Punk Rock
- Sludge Wave
- Overdrive
- Boomburst
- Hex / Volt Switch
Hope I helped!