I wanted to make a thread of all the greatest stallers/walls in the current metagame.
Off the top of my head, I'd say:
Cresselia (120/120/130) , for sheer stats and access to moonlight (Which is generally reliable healing, but unfortunately is nerfed by it's low PP, so rest is generally better.), It didn't gain anything in the generation shift however, so it (Unfortunately) rots in the prison that is the RU tier.
Suicune, (100/115/115) , for consistantly being able to run arguably the most efficient defensive Mono-Attacking moveset in the entire game (A.K.A. CroCune). In the generation shift it gained Scald, which makes it even more deadly by having the possibility to inflict burn, which is especially useful on things that wall it. It also happens to be placed in the UU tier, where it slaughters a lot of top threats, Continuing to be an Insanely powerful pokemon