I haven't been real impressed with my Sonata. The engine and transmissions on NF Sonatas are pretty problem-free. The auxiliary systems are where the real problems are found. The ABS/ESC, airbag and fuel tank emission systems can have issues that are difficult to diagnose, even for the dealer. Mine has had issues with all three systems.
The driving dynamics of it are also not good, on the NF Sonatas, at least.
But, it is quiet and smooth on the highway, and it was cheap. Overall, I wish I would have spent more and bought a better vehicle off the bat.
But it's up to you. Drive them and see if you like them. They generally have worse resale, meaning you can get a newer model for your money.
If you get a Kia/Hyundai, you only get the 5 yr/60k bumper to bumper warranty, you don't get the 100k mile powertrain warranty.