Well, I have shot all of them...although only a couple of mags through a couple of them.
The first I'd eliminate would be the FN, it is just a nightmare to take apart and tinker with.
The best out of the box triggers are pretty much a toss up between the H&K and the Walther...I liked the VP9 better. I really like the paddle mag releases as it is a very natural motion for either your thumb or index finger.
The SIG had the best feel in my hand...I spent years carrying and teaching with a 226 or 220. Out of the box the trigger felt heavy (over sprung) but Grayguns offers a nice drop-in package to address that...Bruce has done all my SIGs.
The SIG 320 upgraded triggers are basically what they are supplying for the M17/18 with the addition of a disconnector. Mine came back with a smoother/lighter trigger and a slightly longer reset. Checking the box for date of manufacture won't help you. Any reputable dealer would have pulled their stock and sent them in to be modified. There is no new production with the modification as they stopped current production to devote capacity to modifying current guns...some guys are getting their guns after only being at the factory about a week..
The two easiest ways to tell if your 320 is up to current spec is the lightened trigger or the disconnector cut under the slide
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