I've only tried healing normal modes on my pala whereas my druid is currently healing FL heroic, so there's a bit of an experience difference there.
Druid - solid raid healer and there's lots of fights (the ones with plenty of aoe damage) that I really feel useful in, the only fight I don't like on my druid is Baleroc and even then it just feels hard, rather than impossible. Can be difficult at lower gear levels, but with Tranquility on a 3min cooldown now it should be easier to deal with spike damage. Make sure you can easily keep track of LB and clearcasting procs as well as time left on cooldowns (tranq, innervate, br etc), when I was first running heroics I had a lot of trouble keeping LB rolling on the tank and what would normally happen when something went wrong is that I'd be busy healing elsewhere, let LB fall off and then be struggling trying to keep the tank alive and the rest of the group and restack LB up, once I got LB monitored more clearly I had a lot less problems.
Paladin - from my extremely limited experience palas seem to be a lot more cooldown based (Guardian, Avenging Wrath, various Hand of ...) and I struggle a bit with mine knowing what spell is best to cast or when there is aoe damage or periods when I need to heal on the move. That's probably more lack of practice though, I spent a long time working on my druid (and considered quitting it for a while) and have healed on it in every expansion, my paladin has always been an alt. They are very strong tank healers and certainly not useless when it comes to aoe healing (plus more cooldowns to reduce raid damage).
You might want to see which class your server needs more, mine is fairly even between the two when the person specifies the class they want.
Depending on gear level you could also try healing with both of them for a time and see which style you prefer.