Neverwinter Nights Cleric
Not an easy choice. They are both strong classes in their own right yet they have even more value in a full party. On top of what metatheurgist already said here are a few other things you may want to consider:
1 - I don't know how familiar you are with NWN and D&Ds, but the Bard's limited selection of spell makes it easier to mess the build if you're not entirely sure of what you're doing.
2 - I'd say that with a good selection of domain, the Cleric beats the Bard handily when it comes to offensive and damage dealing spells, without compromising the rest of their build much if at all.
3 - While Bards are excellent at boosting themselves and the whole party offensively (maybe better than a Cleric at high level) and at boosting themselves defensively, compared to a Cleric they're lacking when it comes to boosting the rest of the party defensively. That being said, the defensive properties that you'll find on several items in the second part of the game will make some of the Cleric's powerful defensive buffs redundant.
4 - Bards have much more skill points per level and access to much more skills than a Cleric. They're a good class if you like to play characters who can talk their way out of stuffs while not compromising their combat capacity, and they can give you plenty of options during that large part in Act 2 with lots of talking (you know the one I'm talking about).
5 - Personally a like having both a Cleric and a Bard since they're both so useful to the whole party. However the OC's Cleric companion joins quite late, maybe pass the halfway point, and while the Bard companion joins around the first quarter he's very much of the hate-it-or-love-it kind. Then in the expansion you'll find a Cleric companion early, but there's no Bard companion at all.
6 - The Cleric version of the OC's plot weapon is actually worth using, while the Bard's version is pretty much garbage. The expansion's plot weapon of either class is hopelessly outmatched compared to crafted weapons anyway.