You asked which one I would pick. I said the Ruger. I am a student, and have to work with a limited budget. Therefore value for my buck is key.
In terms of function, I'd bet that the Ruger just as tough, and just as reliable. Ruger is also known for great customer service, whereas I've heard spotty things about H&K (but I admit- I have no personal experience with either).
Is the H&K going to have a better trigger, and nicer fit and finish? I'd be willing to put money on it. But is the overall difference worth a $350 price difference? Not to me.
The Ruger will be reliable, and put rounds where I want them again and again for a long long LONG time.
To my way of thinking, about $550-$600 is the point of diminishing returns with most pistols(excluding 1911's). At that price, you can get Beretta, IMI, Glock, S&W, CZ, and a host of other high quality guns.
If you pay more, you may get something nicer, but after the point of diminishing returns, it's a disproportionate upgrade in quality.
Edit to add:
That being said, if money was absolutely no object at all, I might spring for the H&K. Then again, I might not if I still go for best value.