If I were multi-boxing a full group, I would not use a paladin healer. They require way too much micro management to make suitable use of the tools they have. The only reason I was successful {my measurement of success} with my paladin healer was the fact that I didn't have to tank. I was able to play my holydin like I was solo healing and dps in the "background". But even then, sometimes you just had to give up on the idea of keeping everyone up.

If I were to do it again, I would probably swap my pally for a resto shammy {vastly superior utility to a druid}. If I were feeling exceptionally motivated, I'd try a priest, as that's the only healing class I hadn't played. But the exceptionally spammy nature of the paladin and lack of group healing/healing options easily puts paladins on the bottom of my healers list, even in solo situations.