They both do the same thing but the acolyte just seems to be more consistent. It costs more but I stopped trying to play the cleric on T1 a long time ago. At best it lives 1/5 times and still rarely manages to give me more than just the one card.
It feels better as a T3 card, or play it at the same time as you heal a minion, to guarantee a card draw. But the acolyte guarantees a card draw anyway. Actually it feels like a really good T3 play because anything with AT2 or less, I can bounce and heal it to keep getting value out of it, or even put PW:S on it.