This may stir it up a bit, but on the average, IMHO ALL Walther models are generally more accurate than guns of similar cost. They have very tight barrel to slide lock up and ergonomics help a great deal to make them accurate. In my experience my P99 QA 9mm is more accurate than my:
Officers ACP, Hi Power, Glock 23, Witness compact 40, Sig 225 & 228, Springfield 1911, Kahr PM, Walther P38 and PPK/s. The only gun that matches it in my accuracy tests is my Walther P5. When I shoot I always have 2 or 3 of the above that I put head to head at different distances just for fun.
I wish I had H&K's to try and the new S&W MP.
That being said though, someone who shoots a Glock all his life and picks up a P99 will probably find the Glock more accurate. Guns are generally more accurate than the shooter. My tagets with my first Glock 17 looked like I was shooting with buckshot as I had no idea at the time what trigger control meant.
You can't go wrong with any of the big names, get what appeals most to you. At the gun store I use two methods to see if a gun is right for me:
1. Close your eyes and aim it at something, open your eyes and see if you are close to target. That means the grip is right for you.
2. Dry fire it once pulling the trigger slowly and see if the front sight jerks in both single and double action.
3. How cool does it look?