First, welcome in the circle of P99 owners !
A few years ago I had the same choice to do. Walther won for me because of its incredible feeling : to have been created for my hand (Thank you M. Morini !). The square shape (even the new one) of the glock was really unpleasant... At the shooting range, it was less obvious : I was more accurate with the glock, it's so easy to shoot. A friend of mine, even not shooter, was able to reach the black part of the C50 target at 25 meters with it. It was more difficult with the P99, the trigger is particular. For my first day with a glock at the same range the worst shot was an 8. With the P99, several shots were in the white part of the C50... I was a bit desappointed...
At short range (7m), the P99 was more efficient and quicker to point. As I bought that gun for a combat gun, I choose the P99. My 357 Manurhin (5"1/4) stays the best to shoot at 25 m, I thought. That was 2 years ago...
Today, I know that it was the good choice. I'm now familiar with the trigger of my P99 and I usually make tight groups, better than the glock at 25 m. At short range it's very quick for pin shooting (the five bowling are down -not down the table, it stays à 9mm
- between 3 and 3,5 sec.). I think it's great for a factory gun.
Some people will say the glock offers more accesories and it's true but what does it mean if the gun fell bad in your hand ? Moreover, there are more and more accesories for P99 too now !
About the reliability they probably are equivalent (both excellent with good ammo).
Enjoy your P99 Dave, be patient at the beginning, practice often, even without bullet, to feel that so special but so great trigger.
Sorry for my bad english, i need to practice too