Blissey has quite a bit going for it. It has monstrous special bulk with its huge HP and fantastic special defense. Its HP makes it able to take a few physical hits even though it has the worst defense in the game. It has a great support movepool, including Heal Bell, Wish, Thunder Wave, and more. Its special attack is not very high, but usable, and is only 10 behind Lickilicky's attack which it will usually be using.
Lickilicky has very well rounded stats. It has a great HP stat, although not as good as Blissey's, and good defenses. It has a very similar movepool, also including Wish and Heal Bell. One thing that it has over Blissey is phazing with Dragon Tail, but that's one of the only things. Obviously, it has supreme physical bulk but is usually run as a special wall.
So, I would use Blissey as a special wall, but if you want a physical wall, try a Pokemon with better physical bulk.