Personally, I'd say Ambipom.
Ambipom makes a decent HM slave like Furret, only losing out on Surf and Whirlpool. Chances are you will have a Water type on your team, and while Whirlpool is questionable, Surf is a good old standby. 1 "dead" move slot isn't going to hamper you for an in-game team.
Additionally, Ambipom can have the ability Pickup, providing you with a relatively steady stream of items to sell for cash, or use in a pinch. As Pickup Pokemon grow in level, they start finding even more beneficial items like Evo Stones, Revives, and in older generations even a few TMs. HG/SS TMs include Fling, Grass Knot, and Earthquake.
Serebii's Pickup table