Personally I would choose Quagsire being that its a ground water type, so electric attacks dont effect it, but Kingler is also good since it can know guillotine (one hit KO move) and knows some ground attacks to fend off electric types. Tentacruel is good too, since it is not highly effected by grass types but instead by ground, electric and psycic types, however since there are soo many pokemon greatly against it, it would not be the best choice, the worst choice would be pollywhrath, being that four types are good against it,electric grass, flying and phsycic.
Quagsire
http://www.serebii.net/pokedex-dp/195.shtml
+ only pokemon good against it is grass types
+ good against electric types
+ HP is high
-grass do times 4 dammage to it
-speed is low
Kingler
http://www.serebii.net/pokedex-dp/099.shtml
+can be good on electric type if it doesn't get hit too much (knows ground moves but still electric and grass are 2x good against it)
+ can learn a one hit KO move
+ Good attack and defence
- Bad special attack and defence
- 2 types are 2x effective against it
Tentecruel
http://www.serebii.net/pokedex-dp/073.shtml
+high HP, Special defense, and speed
+is part poison so good against what poison is good against.
- 3 types are 2x effective against it
Poliwrath
http://www.serebii.net/pokedex-dp/062.shtml
+ is part fighting, so good against grass etc..
+ good HP and good Defence
- 4 types are 2x effective against it