Faced with the same conundrum, in the past month I have sold off several of my "dust collectors" and purchased two of the three of the handguns in question - an HK P30S V3 and a Walther PPQ M2 Navy. I also picked up a Beretta APX and an AREX Rex Zero 1 (SIG P226-ish, but superior, IMHO). Right off the bat, toss out the Beretta - the trigger is plain horrible making my example difficult to shoot well despite the excellent ergonomics.
In my view the HK SFP9 is nothing more than a striker-fired P30. Decide which action type you prefer, then go for it. I personally prefer a Hammer-fired double/single-action with it's more deliberate first shot and "second strike" capability in the event of a light primer-strike. THE P30 Version 3 provides such a trigger and is what I bought. The P30 version with the Law Enforcement Module (LEM) trigger will provide you with a (long) single-action-only type of trigger pull with the same "second strike" hammer-fired capability as the double/single action. The striker-fired SFP9 does not offer "second strike", but does provide a consistent trigger pull similar in weight and feel to a single-action. It all depends on what type of trigger action and pull you prefer. Everything else flows from that In terms of each pistol's fit/feel in the hand and the desired festures (decocker, manual safety, etc).
Once you decide which action type(s) you prefer, it is time to go shopping and seriously compare the features, EE prices, add-ons (eg. Spare mags), and so forth. I prefer hammer-fired and double-single action, so that Settled the P30 versus VP9/SFP9 question for me. I went with the P30S due to the shorter slide and factory threaded barrel being a bit more rare on the international market. Other options abound, as you can have a manual safety (or not), the "single-action-only" LEM trigger or a double/single action, a threaded barrel or Long Slide, etc.
If you want to try the highly-regarded Walther PPQ line, there is no choice of action type as they are all striker-fired with an excellent, crisp trigger, but no "second strike" ability (without a partial slide retraction). The biggest advantage of the PPQ Competition model is that it comes pre-milled for various MIni Red Dot Sight (MRDS) options. The slide is lightened (but not compensated) to compensate for the MRDS's extra weight. You pay a significant premium for the MRDS cut. If you can live with a Vortex MRDS instead of say, Trijicon, you can go with a direct dovetail MRDS mount for under $60 USD and save yourself several hundred $$. I went with the PPQ M2 Navy because it comes with the extra feature of the longer, factory-threaded barrel. All other factors being equal, the biggest single draw of the Walther PPQ line is the outstanding "pre-cocked" striker-fired trigger.
Then there is the AREX Rex Zero 1, which is basically a double/single-action "SIG P226" with a manual safety. The Rex Zero 1's build quality easily rivals that of any West German SIG that I have ever owned (2 x P226s, P227, P220, etc). The mechanical-disconnnect safety of the Rex offers additional carry options that the P226 does not, such as "cocked and locked" single-action. All weapon manipulations can be carried out with the safety engaged, enhancing operator safety. The double-action trigger is heavy (12 lbs), but very smooth, short and crisp. The factory light spring kit addresses the heavy double-action pull. The single action trigger pull is crisp and short at 5.5 lbs. Aside from a somewhat chunky P226-dimensioned grip compared to other pistols with customizable back-straps and Grip Panels, the Rex Zero 1 is simply outstanding in most every regard. If you are a fan of the SIG P226 double/single action, you will most likely love the Rex Zero 1. It is easily on par with my P226 Legion SAO in terms of practical accuracy and that is really saying something. The Rex Zero 1 "Tactical" adds useful features (pre-millled slide for MRDS, extended/threaded barrel) for a premium price of approx $1300 CAD ($930 for the regular model). You didn't ask about the Rex, but it is definitely worth considering if double/single-action is your preferred operating system.
The only other pistol I intend to pick up at this point is the new Glock 19X when it comes to Canada. I view the 19X as the ideal blend of G17 and G19 features, in effect the "ultimate" Glock. I sold my Gen 4 G17 to make room on the rack.
One modern 9mm that I absolutely CANNOT recommend is the basic SIG P320. I say this entirely because of the stock trigger, which was absolutely horrible on the example that I owned. Heavy, with a brutal "stack", I had to "load" the trigger for each careful shot. Attempts to rapidly fire were a dismal joke. How anyone could "run and gun" with that trigger is a mystery to me. I could care less about reliability and ergonomics if the trigger is so brutal that I cannot get past it. Other examples of the P320 that I have tried out of idle curiosity were no better. The only SIG P320 with a decent trigger (in my view) is the X5 with its factory-tuned version. That, and the improved ergonomics of the X5 grip, will set you back a cool $1300 CAD. Until APEX comes out with a decent after-market P320 trigger, the X5 will be the only 320 Trigger Group worth owning IMO. YMMV, of course.
HK P30S:
Walther PPQ M2 Navy:
AREX Rex Zero 1 Tactical:
