Just looked at the map:
1. Hoenn is still the king in my opinion
2. Kanto, the original
3. Johto, cool region but very small
4. Unova, was okay but way to linear
5. Sinnoh, not my cup of tea. It was a boring region everything was putted way to clean/nice.
For Karos, it think it will be between Hoenn and Kanto I'm content.