WHM perspective, I don't heal very often on my SCH aside from a few dungeons here and there.

With big pulls and multiple mobs I prefer to heal a Paladin, mostly due to the fact they are easier to heal during this time thanks to their Shield, Invuln, and a wide variety of cooldowns. I've found for the most part with a good Paladin I can spam Cure 1's with Regen and keep them up relatively easy on big pulls 8+ mobs. Maybe throw in a few Cure 2's when cooldowns are coming off, but nothing overly major.

Where as with a Warrior I have to spam Cure 2 non-stop just to keep them from dieing. Even with their cooldowns, it's just harder to keep them alive. Now don't get me wrong, critting for 4K (no cooldowns/buffs) Cure 2's on a Warrior is awesome, but still.

In a typical raid setting it can go either way, although typically I'm the designated healer for the Warrior just because I have an easier time getting them to full HP.