Realize that the SW99 is the same gun as the Walther P99 A/S. But, the SW99 was discontinued at the end of 2005. Although, U can still buy them new.
The SW990L was still in production as of Dec 2007, but I think S&W will discontinue it soon, personally. They will want to push the M&P more. Anyway, the SW990L is the same as the P99 QA trigger, only it has no decocker button at all.
I have owned a SW99 up until recently, and I have 2 P99s. I prefer the P99. It looks better, and the grip IS slightly different - the P99's grip is better IMHO.
Also, before I decided to sell my SW99, I did comparison shooting many times, and my P99 A/S was slightly more accurate than the SW99. However, the SW99's triggerw as a tiny bit better. But, that can vary from specimen to specimen of the same gun.
If U can get the Walther, go ahead.
I only bought the SW99 because Walther stopped importing the P99 A/S for a few months in 2005. After I got it, I stillw anted the original....