Thought you'd toss out one those easy-to-answer, non-debatable questions, did you?
Okay ...
Yes, No & Maybe.
I own a number of different 'working' pistols in 9mm, .40 S&W and .45 ACP, and over the years I've been issued a number of different pistols, of different sizes and magazine capacities, chambered in the same calibers.
After a number of years as a LE firearms instructor and armorer I finally decided that caliber and capacity matter less to me than reliability, inherent practical accuracy, ease of maintenance/support and overall ergonomics.
After a number of years of carrying a 15+1 9mm service pistol I opted for the compact 12+1 model after working a plainclothes assignment for a while. If I'd had the opportunity I'd have selected one of the few 3913's available for their slimmer and lighter 8+1 single column features, and I'd have been comfortable carrying one for either uniform or plainclothes, but they were designated for folks who just couldn't use the standard pistols with wider double column magazines.
So, I guess sheer 'capacity' wasn't as important to me as it might be to some other folks. Neither is caliber. Not really.
I was later issued a full-size .40 S&W with 12+1 capacity. I eventually decided the issued 9mm compact with 12+1 capacity was preferable to the full-size .40 S&W of similar capacity, albeit larger caliber, so I chose to carry the 9mm pistol more than the .40 S&W pistol. Equal capacity ... but I chose the 'smaller' caliber for the platform, for reasons of personal preference considered from training and daily carry experiences.
I later turned down an opportunity to carry a standard steel 7+1 capacity Colt pistol, one of our few special purpose pistols, and did so simply because of the weight. After I was later issued a TDA 8+1 capacity all-steel .45 ACP service pistol, and carried it in my plainclothes assignment for a while, I finally turned it in so it could be issued to someone I knew who really wanted one of the new all-steel .45's. He was very pleased with it, and I chose to carry an issued lightweight compact 9+1 capacity .40 S&W.
I suppose you could say I traded a larger, heavier 8+1 capacity .45 ACP for a smaller, lighter weight .40 S&W with an additional round's capacity ... but I chose it not for the capacity, but for the lighter weight and ergonomics, both of which were simply preferable for me.
Now, I'm not exactly consistent in my preferences, and I'll admit to that ...
For example, I'll chose to carry a J-frame with 5-shot capacity over my CS45 with 6+1 capacity ... and do so for reason of the lighter weight and smaller size.
Then, on another day when I do chose to carry a pistol off-duty, I'll chose the CS9 over the CS45 ... because the CS9 is slightly smaller and lighter, and has 7-rd magazines instead of 6-round magazines.
Some days I'll chose for overall size & weight ... other days for specific caliber ... and yet other days 'capacity' might be more of a consideration ... and then some days for overlapping considerations of all of the above.
Never said I was consistent ...
I do tend to like the .40 S&W and .45 ACP for their heavier bullet weights, although I don't lose any sleep when carrying lighter bullet weights in 9mm or .38 Spl.
Matter of fact, I'd still choose to carry an issued 9mm if that were an option. I've fired many ten's of thousands of rounds of 9mm downrange over the years since we originally transitioned from .357 Magnum revolvers to 9mm pistols, and I feel confident in using it for defensive purpose. It's not an option, however, since the decision was made that our new issued weapons will only be offered chambered in .40 S&W and .45 ACP. Oh well. No big deal. I still choose a 9mm more often than a .40 S&W or .45 ACP when it comes to choosing from among my personally owned off-duty weapons.
Now, if I were offered a choice between an issued P220 or a P226, I'd consider most of the same factors. Does one 'fit' my hand better than the other? Do I prefer the way one handles, balances and shoots more than the other? I'd carry either as an issued weapon and not worry about it, but if I had a choice and an opportunity to try both, I'd try them and then make my decision for whatever reasons suited me and my perceived needs.
It's just a handgun, chambered in one of the major defensive LE calibers ...
Not much help, huh?