I think Kingdra and Chansey are the top two defensive Pokemon. Kingdra with either resttalk or haze walls a lot of stuff, although I'm inclined towards Resttlak with Dragonbreath for para. Curse Kingdra is walled by DB Kingdra and by other cursers.
Chansey runs either Heal Bell or a more supportive set with Thunder Wave / Reflect / Screen / Toxic / Sing etc. Don't know if using an attack is worth it...
I think the other top 3 is Quag: With Kingdra/Chansey/Slowbro being UU, the meta is much more balanced/defensive, and Drumquag abuses that. I feel HP Grass could become the top choice for electrics, given that Kingdra with resttalk easily walls Nidoqueen.