Shen or Poppy. Whose the better Peeler Tank?

In a general perspective? Poppy. Her W and Ult are just big "no"s to enemy Assassin and Dive Fighters, and unless you are very specifically using her in an aggressive fashion, it's a little harder to utilize her CC in a non-defensive manner, whereas a Thresh player likes initiating with their Hook Ult Flay combo. If you intentionally play defensive however, I'd say both are on somewhat equal terms.

even though I like Shen more, I have to agree with TheNACHO, while Shen can peel, he's more situated for engaging.

Amateurs. Let the saplings have their limelight. They'll get theirs soon enough. ----------Meanwhile---------------- Haha snort smiles

Both are average peelers, many supports do it better. I would say Poppy does it better than Shen, but neither of them are the best at peeling.