Having owned and shot both, the P229 wins..
Excellent ergos, flawless reliablity, accurate and not needing any tinkering..
The P99 is a fine gun too...IMO it's what a Glock should have been. Excellent grip, good accuracy, relaible.
The controls are a bit funky. It takes a bit to get used to the mag release, which if you all you shot were guns button type mag releases, then you will have a tough time...I did. The de-cocker is a bit of a reach if your hands are small...being on the slide makes it hard.
Both are great guns, but for a combat carry auto, go with the P229