Hello. I own a Walther PP and have owned a couple of PPK/S pistols as well. I currently have a SIG-Sauer P230, a CZ-83, and a Bersa. The Walthers and CZ have steel frames while the P230 (blue version) and Bersa have aluminum frames. I suspect strongly that if one did a torture test to see how many rounds each would fire before something gave, the steel guns would probably win.
In my case, the Bersa has run 100% for over 3K rounds and close inspection shows no cracks, abnormal wear, and there has been no small parts failure. The feed ramp is scuffed a bit, but not gouged. This is due to my using primarily ball and JHP's having rounded ogives.
I really appreciate the cocked-and-locked capabilities with the CZ83 and mine's proven reliable with every round I've tried except the Federal 90-gr. Hydrashok.
It is, at least, reliably unreliable with that particular round. All others have functioned 100%.
The Walthers I own bite me when fired due to the low slide and my fat hands.
My German/French PP .380 is somewhat picky with regard to JHP ammo. It also has the worst DA pull of the bunch. An old Walther PP .32 I bought from a guy needing money more than the gun has a superb DA pull so perhaps it's just my individual Walther .380 that has the substandard DA pull.
If interested, here's some observations concerning the Bersa vs. SIG-Sauer P230:
http://www.hipowersandhandguns.com/Sig Sauer Bersa.htm
I personally find the Bersa the most comfortable of the guns you specify, but that is subjective and does not mean that I find the CZ or SIG-Sauer uncomfortable.
For my needs and because I do not shoot .380 nearly so much as other rounds, my personal pick would be the Bersa. If you like the pistol but have concerns over the aluminum alloy frame, I THINK it's also available with a steel frame.
Here's an older report I did on the CZ-83. Perhaps it will be of some use:
http://www.pistolsmith.com/viewtopic.php?t=13241&highlight=range+report
My choice certainly is not the only one nor is it any more right or wrong than others. I do believe the Bersa to be a best buy at the current time.
Good luck in your query and best.
PS: Since the report on the CZ was done, I have recorded some chronograph results with various loads:
CZ83:
Glaser 70gr Safety Slug(Silver) Ave. Vel.=1299 (ES: 116/SD: 44)
Magtech Guardian Gold +P
85-gr JHP Ave. Vel. = 1075 (ES: 33/SD: 10)
Federal 90gr JHP Ave. Vel. = 1017 (ES: 48, SD: 17)
Federal 90 gr Hydrashok Ave. Vel. = 1036 (ES: 80, SD: 23)
Hornady 90 gr XTP Ave. Vel. = 933 (ES: 42, SD: 14)
Corbon 90gr JHP +P Ave. Vel. = 1083 (ES: 45, SD: 17)
Magtech 95-gr FMJ Ave. Vel. = 964 (ES: 29, SD: 10)
Remington UMC 95gr FMJ Ave. Vel. = 970 (ES: 32, SD: 9)
Remington 102-gr Golden Saber Ave. Vel. = 928 (ES: 70, SD: 22)