Personally,
When I am tanking and what I hear from other MAs is that they prefer dark elves. The reasons for this, I believe, are three fold:
1) DE clerics are KOS in most places throughout Norrath. This forces them to be savvy with their invulnerability, gate, and lull spells to get around. This makes them good for pulling (yes, pulling!), staying put to take a few hits while the tanks get aggro or the casters mez/root, and they tend to be commited to group soidarity and dynamics because they have run afoul of many KOS guards while out on their own. Hardship is a good teacher.
2) The DE cleric symbol quests result in an insta-clicky snare DOT (clinging darkness) item. Because druids and necromancers (those with slow spells) are often out soloing, a group is thankful for this interesting extra. It makes crowd control, pulling (there it is again!), and running to the zone line on a bad pull much easier.
3) Pulling! Well, sorta. Dark Elves have a high agility. Combined with the cleric's ability to wear plate armors, the DE cleric tends to have a higher Armor Class than other races. The dwarf is also a good choice in this case because of their high stamina and thus, higher number of hit points. In a typical group, your vital elements are a tank, a healer, and some crowd control. If your healer is able to take hits, one of your vital elements is less likely to disappear.
that my 2cp,
-Forzz, 38 CLeric of Innoruuk, <evil legions> drinal