Ok, here goes...
Quagsire
Type: Water/Ground
Abilities: Damp, Water Absorb & Unaware (HA)
Movepool: Good
Stats:
- HP: 95
- Attack: 85
- Defense: 85
- Special Attack: 65
- Special Defense: 65
- Speed: 35
- Total: 430
Swampert
Type: Water/Ground
Abilities: Torrent & Damp(HA)
Movepool: Good
Stats:
- HP: 100
- Attack: 110
- Defense: 90
- Special Attack: 85
- Special Defense: 90
- Speed: 60
- Total: 535
Gastrodon
Type: Water/Ground
Abilities: Sticky Hold, Storm Drain & Sand Force(HA)
Movepool: Average
Stats:
- HP: 111
- Attack: 83
- Defense: 68
- Special Attack: 92
- Special Defense: 82
- Speed: 39
- Total: 475
Seismitoad
Type: Water/Ground
Abilities: Poison Touch, Swift Swim & Water Absorb(HA)
Movepool: Very Good
Stats:
- HP: 105
- Attack: 85
- Defense: 75
- Special Attack: 85
- Special Defense: 75
- Speed: 74
- Total: 499
Whiscash
Type: Water/Ground
Abilities: Anticipation, Oblivious & Hydration(HA)
Movepool: Average
Stats:
- HP: 110
- Attack: 78
- Defense: 73
- Special Attack: 76
- Special Defense: 71
- Speed: 60
- Total: 468
Stat Comparisons
HP
1st: Gastrodon (111)
2nd: Whiscash (110)
3rd: Seismitoad (105)
4th: Swampert (100)
5th: Quagsire (95)
Attack
1st: Swampert (110)
2nd: Seismitoad & Quagsire (85)
4th: Gastrodon (83)
5th: Whiscash (78)
Defense
1st: Swampert (90)
2nd: Quagsire (85)
3rd: Seismitoad (75)
4th: Whiscash (73)
5th: Gastrodon (68)
Special Attack
1st: Gastrodon (92)
2nd: Swampert & Seismitoad (85)
4th: Whiscash (76)
5th: Quagsire (65)
Special Defense
1st: Swampert (90)
2nd: Gastrodon (82)
3rd: Seismitoad (75)
4th: Whiscash (71)
5th: Quagsire (65)
Speed
1st: Seismitoad (74)
2nd: Swampert & Whiscash (60)
4th: Gastrodon (39)
5th: Quagsire (35)
Total
1st: Swampert (535)
2nd: Seismitoad (499)
3rd: Gastrodon (475)
4th: Whiscash (468)
5th: Quagsire (430)
Overall
I would definetely go with Swampert because of its great movepool, abilities & stats, while Quagsire, Gastrodon & Seismitoad all would come second
Hope I helped!!