Clefable is obviously a beast with its moveset and even bulk, but if you are looking for a bulky staller, Chansey is they way to go. Both can be used in the same team, if you train them well and provide the best moves. I admire both, but I prefer Clefable because it has a great Movepool, and Chansey has a defense worse than a jack rabbit on a hard pickle. For a Clafable in general, I would recommend the following:
Clefable Item: Leftovers
252 HP/172 Defense/84 Speed
Nature: Calm/ Ability: Magic Guard
Calm Mind: Improves special defense and accuracy, leading to an increased amount of stamina.
Moonblast: After Calm Mind is used at least once, this move will be devastating beyond control.
Soft-Boiled; Used for gradual health recovery over time, this will be helpful for this Clefable based on its EV's.
Thunder Wave/Flamethrower: Both of these can be used for coverage over Clefables weak spots.
Clefable is obviously amazing both defensively and offensively, but Chansey is most definitely not to be excluded. I would use an Eviolite Chansey as a Toxic/Soft-Boiled/Protect Pokémon for its amazing capabilities. I have used this in combat before, and it has not let me down.
Chansey Item: Eviolite
4 HP/252 Defense/252 Special Defense
Nature: Bold/ Ability: Natural Cure
Toxic: A great move to slowly kill your opponent. This corresponds with Chanseys EV's and other moves very well in this case.
Soft-Boiled: A way to quickly recover health like Clefable. This can easily be used with Chanseys amazing Bulk.
Seismic Toss: Mainly included in this Moveset for the Purpose of breaking substitutes, and can be beneficial with Chanseys terrible Attack stat.
Heal Bell/Stealth Rock/Protect: All of these are great for this Pokémon, though I would advise using either Stealth Rock or Protect. Stealth Rock for setting up a way to damage your opponent and negate Sturdy, and Protect to improve Toxics effect drastically.
Chansey and Clefairy are great options, and whichever one you use is greatly determined by the other components of you team. Choose wisely, and good luck.