Surprised no one's mentioned Grand Power's rotary barrel pistols yet... Especially given they're made in Slovakia and the most like a CZ in the hand...
Beyond that, here's my quick take:
- PX4s reassembly is a fair bit easier than Grand Power, although I have a first gen GP with the pull down trigger guard instead of Glock-style button currently used, so it's probably become easier but not as easy as the Beretta
- Grand Power tends to fill the hand more and has a longer length of pull due to both actual longer length and increased angle meaning length is also longer (I haven't tried all grip panel sizes for both side-by-side, but think this assessment will hold)
-- by increased angle, you can get a higher grip on GP than PX4, so PX4 is more of a straight-to-rear pull like a Sig, while GP is more of up and to the rear like a Glock, so accounting for the angle the distance is also longer if you have a proper, high purchase grip on the GP
-- higher grip purchase is a plus for GP in my book
- PX4's safeties are familiar to Beretta users as well as classic Walther and Bersa Thunder shooters, while Grand Power safeties follow the CZ, 1911, etc., function of up for safe... My GP is safety only and haven't seen decocker model in real life, while PX4 safety model does both safety and decock OR exclusively decock -- so GP can be "cocked-and-locked" while I don't believe the PX4 can be; while GP also can't be decock-only AFAIK (from vids I've seen, the decocker is dual safety and decock).
- I don't like GP's polymer-only trigger (haven't seen aftermarket metal) and the slide release feels cheap being stamped sheet metal... Otherwise, the GP finish is superb and I daresay slightly better than PX4's on the whole.
- This also reflects more aftermarket parts and support for PX4 vs GP, such as sights and safety levers/function and trigger mods.
- GP has a better trigger out of the box in standard configuration IME, though with aftermarket, PX4's can probably be made as good or better.
- PX4 is more compact for concealed carry.
- At this point, they're about the same price, but I picked up my GP for something stupid-low ~$300 when JG Sales was clearancing them out after Century ceased being their importer about a decade ago now... However, if you can get the PX4 with a Beretta rebate, it's likely a better "deal" at low to mid $400s.
All in all and ergonomics/manual of arms differences aside and irrespective of price and between just these two, I think Grand Power has an edge as a competition or duty gun, while PX4 has an edge for concealed carry, new and more feeble shooters (where ease of use and maintenance is essential), and an heirloom gun w/ guaranteed parts and support given it's made in the USA.
To be clear, however -- I think ergonomics/manual of arms standardization should be at the forefront of decision-making for any serious-use weapon, in particular how each points for you and how the controls operate vs. what you've trained or used most to-date.
Caveat emptor -- I don't own a PX4 yet and have only handled at the gun counter, but am heavily leaning towards acquiring one in 9mm for the Mrs as she continues to build shooting skills and confidence, and would benefit from the rotary barrel and easier maintenance as she moves up to a more capable caliber... And FWIW, this thread and some related research has helped me to feel more comfortable heading in that direction.
For visual folks, here's a handgun hero side by side:
https://www.handgunhero.com/compare/beretta-px4-storm-compact-vs-grand-power-p1(Used it to confirm PX4 is in fact more compact than compact GP -- mine's full size...)
As always, YMMV.
