Which is better and for what purposes.
Edit: it won't let me use the tags clefable, wigglytuff, or jigglypuff
Both Clefable and Wigglytuff perform different roles in the metagame. But there is a reason why Clefable is RU while Wigglytuff is NU.
Clefable can run a multitude of sets due to its access to Magic Guard, which make it take no damage from status; only direct damage can hit. Therefore, it can absorb status and support the team with Wish, Heal Bell, and Stealth Rock. Having better Defenses than Wigglytuff make sit a better team player. Having Magic Guard means it also takes no recoil from Life Orb and recoil moves, meaning offensive Clefable with Double Edge can put in work.
Wigglytuff's main perk is that it has a large HP stat, making it an effective Dual Screener and Wish Passer. It can also set up Stealth Rock. Besides that, Wigglytuff is outclassed by Clefable.