With Ulduar due to hit in the near future, Tales of a Priest addressed a pretty timely subject for 25-man raiders yesterday with a blog post on Val'anyr and how you're going to assign it. As it's a constructed Legendary like Atiesh rather than being a dropped item like the Warglaives and Thori'dal (sudden thought: why do the caster Legendaries have to be assembled, whereas the melee/ranged Legendaries just drop?), you're going to have to put some time and thought into which one of your healers is going to get this baby first.
It's not exactly the world's most comfortable question for a guild leader, but I like how Derevka lays the issue out so matter-of-factly, and then goes on to address an interesting point concerning Val'anyr's proc. Your ideal candidate is a good healer with great attendance who plans on hanging around for a while, but then there's the question -- which class gets the most use out of the proc?
Between Derevka's commentary and a few notes from the Wowhead thread, it does seem as if Paladins and Discipline Priests are the classes/specs most suited to Val'anyr's shield proc. This is somewhat disappointing for me as a Druid, but then, nothing about the mace is set in stone until 3.1 actually goes live. How is your guild deciding how to assign this much sought-after piece?