With kia it makes no difference. They have a set service schedule per mileage etc. and that's that.
However, with Amsoil you'll get a warranty with extended oil changes. I've been doing this for almost 25 years with no issues and I use the Amsoil filter.
5W-20 XL would be a good selection for your car.
AMSOIL - Extended Life 5W-20 Synthetic Motor Oil (XLM)
In the following thread I've laid out some info that might help you. At the very end I've also laid out some of the service intervals I do with my equipment and for many of my customers.
http://www.kia-forums.com/do-yoursel...hetic-oil.html