Hi Saturn, I haven't tried the SP330, but I do have the SP540. I think they are quite comfortable with a nice sound to them. I'm not trying to steer you towards a higher-priced model, btw.
Just chiming in with my experience with one of their newer headphones. For whatever reason, I never really thought of Koss being quality gear, but I was really impressed overall by the SP540s. I'm not a headphone expert, so take that as you will.