Sharpedo
- Quite fast
- Amazing Attack stat and respectable Special Attack
- Solid Ability in Rough Skin
- Naive is a very good Nature for Sharpedo
- Learns moves like Crunch, Skull Bash, and Hydro Pump
- Dark and Water are special in Gen 3, meaning it doesn't get to effectively use its better attacking stat
- Paper-thin defenses
Walrein
- Excellent tank, with 110/90/90 defensive stats
- Thick Fat ups its tankiness even more
- Solid Special Attack
- Water and Ice are special in Gen 3, meaning it can use its better attacking stat well
- Learns moves like Waterfall, Surf, Blizzard, and Ice Beam
- Gets zero special moves that aren't STAB, meaning you'll have to do a mixed moveset
- Modest and a mixed moveset isn't a good combo, but it works
- Fairly slow
If you want a speedy attacker, go with Sharpedo. If you want a hard-hitting but slower attacker, go with Walrein. I'll provide sets:
Sharpedo @ anything
Ability: Rough Skin
- Waterfall / Surf
- Crunch
- Strength / Return
- Skull Bash / Earthquake
Walrein @ anything
Ability: Thick Fat
- Ice Beam
- Surf
- Earthquake / Strength
- Return
Hope I helped!