I know from experience that bulky Quagsire with Water Absorb isn't the best choice as a Water/Ground. Swampert's ability (Torrent) isn't as good, but it has better stats for full-on attack than Quagsire does (which has horrible Speed). I would only suggest using Water Absorb Quagsire in Double battles with something else that knows Surf.
However, Quagsire is probably more useful than Swampert due to Unaware. Quagsire's stats are indeed less than Clefable's, but mostly just by Speed disadvantages. Clefable has a horrible stat-boosting movepool, and can learn a lot of stat-lowering moves, which makes Unaware a flaw. Quagsire on the other hand, had less weaknesses, and can learn Amnesia, Curse and Recover, which are great with Unaware, as opponents' stat boosts won't be able to level with it. Add a physical attack to that, preferably Waterfall (Earthquake would be very powerful with Quaggy, but if you give it all three of the status moves I've listed, Quaggy would be useless against Flying-types). Rocky Helmet would be a good item because if you get high enough Defense boosts, the opponent would do more damage to itself if attacking physically. Curse is good with Quagsire because its Speed stat is only useful if it's being Trick Roomed. As for the Rindo Berry, Recycling it would only waste a turn, so whatever Grass-type attack hit Quaggy first will likely wipe Quaggy out on the next turn.
To put it into one sentence, Unaware Quagsire is better than Water Absorb Quagsire or Unaware Clefable.
Quagsire is my favorite Pokémon anyway, so who am I to complain?
