Ok I will do a comparison.
Pros: High HP and decent defenses as well as the classic large normal type movepool.
Cons: Though his Defenses are decent they are not great and even Garchomp has higher overall Bulk, so he will not take very many big hits.
Role: Support or possibly a Calm-mind tank
Pros: Gigantic HP and great S. Defense and boostable S.attack, great movepool, and Great abilities.
Cons: Defense is Pathetic, a strong Physical move will 2KO if not OHKO her.
Role: Wall, Especially Special Wall, Calm-mind tanking is possible, and Support
Overall Blissey is the better choice but remember Blissey is trapped in OU while Audino can be used in UU(The new one) where there is no Blissey or Chansey.