for personal use as well as work use, I use an Intuos 3 (9"x12") with Photoshop:CS and have never experienced nor heard of these mentioned problems with smooth lines. if you're really looking for something new, I give personal recommendation. obviously the 9"x12" size is not a requirement, but from what I've heard compared to what I've experienced, the intuos line of products is excellent.
painting with intuos 3 and ps6 (before I had cs):
I'm no master painter, and I definitely dont get paid for this, but having the right tool for the job helps me pretend it.