I have a 99 Sephia, which I don't think they make anymore. We've had a few problems with it, but were taken care of without a problem. I don't think I would ever buy a used one, but new with the ten year warranty. When we finish paying off the one we have, we will probably purchase another Kia. My DB and SIL also have one, but they put alot of miles on theirs and have had some more significant problems.
I really have no complaints about mine...its no frills in the Sephia, but DH uses it primarily for commuting and it gets good mileage.