HK makes a great weapon, but in making your decision, I would ignore the fact that the HK has a hammer, and quite possibly the decocker location too. You'll quickly grow accustomed to the P99's decocker if you get an AS. I can get it with the thumb of my shooting hand, or my other hand.
Glock is undoubtedly the king of handguns today, they are striker fired like the P99 is. "A hammer does not a good pistol make." I would also say that most people, at least myself anyways, fumble to thumb the hammer on medium to large semiautos. I can't, for the life of me, cock the hammer with my strong shooting hand on a buddy's Sig P229 without fumbling with the gun. I also have a bit of a hard time with my PPK/s without adjusting my grip. Do I have small hands???
If you're looking for a quick way to cock the P99 AS, you simply retract the slide about 3/8" and release. It doesn't eject the round in the chamber, just sets the striker to single action "AS" mode where the trigger is light and in the forward position. You can carry in a good holster in this mode.
Alas, you hit the nail on the head with Smithy not importing the AS trigger setup anymore. As long as you like 9mm, I believe you can still get 'em from Earl's, though I hear he's a dick and I know his prices are outrageous.
Speaking of prices, it has been my opinion that HK makes great guns, but they tend to be overpriced cause they happen to say HK on the side! Throw in that crappy mag release (I think the P99's is MUCH more ergonomic for my hands), and I think you'll see that the P99 is probably the better buy, even if you have to get the QA trigger (not bad, just not an AS). Besides, the P99 just LOOKS cooler.
Sorry to give a biased answer, you're on the walther forums after all... heheh
P.S. if the prospect of a QA type trigger doesn't bother you, you should also look at the excellent Springfield XD line of pistols. Fits the hand similarly to the P99, and costs less money. It even has a grip safety, like an 1911, and shoots wonderfully, to boot!
EDIT: spelling, it is early in the morning