Of the list you've posted I have direct experience shooting Glocks (17, 19, 26), the Walther PPQ and the SR-9.
Glocks are a known standard. Their reputation for durability and reliability is the stuff of legend. If anybody makes parts and accessories for handguns that aren't 1911s, they probably make Glock parts. They are actually capable of greater accuracy than most generally give them credit for. Note: I've owned and shot Glocks as my primary centerfire semi-auto pistols for the last 14-15 years.
The Ruger SR-9 is merely OK in my book. They work, they're not expensive, and they're fairly trim, that's about all I have to say. If somebody on a budget was looking for a reliable, full-size 9mm striker gun, I'd suggest the SR-9E without losing any sleep.
Now, the Walther PPQ. Fair warning: Oh boy oh boy, do I LIKE this pistol!
I describe the PPQ as a Glock that's been through finishing school. It's significantly easier to shoot accurately straight out of the box. The trigger truly is as good as all of the reviewers blather on about. The stock sights work better for me than the stock Glock sights (though neither are particularly stellar). I can make hits on smaller targets faster than with a Glock. As a bonus the Walther naturally indexes very well in my hands, making it much easier to hit things while on the move. My particular PPQ is an M1 and has been more reliable than my Gen 4 Glock 19. Glock 19: 570 rounds between stoppages. Walther: No stoppages to date, though the round count is fairly low, a little over 1000 so far.
(I just noticed how important that "much easier to hit things with" facet is for me after writing that.)
Cons to the Walther: parts and aftermarket support are not as plentiful as with the Glock or an HK. You can find sights, holsters and magazines relatively easily, but you won't have your choice of styles or manufacturers. You also have to be sure to get the correct magazines concerning the M1 versus M2 magazine releases. Some of the M2 buttons are reported to benefit from a stronger spring to prevent accidental magazine release.
Next up on the list, I would really like to get a VP9 to live side-by-side with the Walther.