Chansey. As Codeine Kiss already told, Clefable was not that useful until it got Fairy-type.
What Smogon says about Clefable (RU):
However as with everything, Clefable has its flaws. The lack of useful resistances--Normal-types only have one immunity, to Ghost-type moves--hurts its, as it often finds it difficult to wall very strong special attacks. Another drawback is its somewhat low physical bulk and weakness to Fighting-type moves, which makes its very vulnerable to strong physical attackers, Fighting-type Pokemon in particular.
And in UU:
> Unfortunately for her, the new generation has not been so nice. She no longer has a niche with Magic Guard; Sigilyph and Reuniclus have usurped her throne as the queen of "who cares about residual damage?" Throw a UU-cast Mew into the mix with an impossibly incomparable movepool, and Clefable finds it harder and harder to stand out among the crowd.
So you can tell that Clefable has many flaws which hinder its usability as a Wish support, most notably its Normal typing.
And Chansey:
While Chansey was once completely outclassed by her older sister Blissey, Eviolite has transformed her into one of the most bulky Pokemon in the entire game. Eviolite boosts both of Chansey's defensive stats by 50%, making her a fantastic mixed wall. The only downside to holding Eviolite is that it forces Chansey to lose out on precious Leftovers recovery; however, this is essentially a non-issue, as with an efficient EV spread, Chansey is still able to take hits better than Blissey ever could. As if all this weren't enough, Chansey is able to act as an amazing team supporter thanks to Wish's new mechanic, which heals teammates with 50% of the user's max HP. Since Chansey's HP stat is tremendous, she can pass massive 352 HP Wishes to any Pokemon on her team, keeping them completely healthy throughout the duration of the match.
Wish Chansey is a really good Pokemon for your team. Even if it is UUBL, it can do good in OU. Just ensure that your enemy doesn't throw a Substitute ghost-type like Gengar. And about it getting weared down by toxic, it gets Natural Cure for getting rid of its status and Heal Bell for its allies.
