If you have a P365...I would vote "neither" (I've owned both a 43X and a 26) and would instead explore other options.
For example, a Talon grip panel may help if you need more girth. The Wilson Combat grips for the P365 and P365XL are also "rounder" (although the trigger reach is about the same). Some have good luck with Hogue grip sleeves. Hockey tape might be worth looking at. Or simply swap the fcu into a P365XL grip module, and poof, you have a P365X. Going up the scale quite a bit would be using an X Macro grip module, but that get's you into G19 territory, but with 17 round mags and more than likely a swap to the XL slide (although a P365 slide will work, just looks stubby).
Now if you've considered all those already, of the two options, I'd pick the 43X all day every day and twice on Sunday (actually I preferred the 48). However, comma: I found the 26 carried with 12 round OEM mags about the same as a G19, so I did. Which made the 26 redundant. It's also heavy, relative to capacity. I sold it without any remorse. I found the 43x very snappy with carry ammo (GD 124+p), and even a tungsten guide rod (net +0.9 oz) from Lenny did not help. I would say the 43X was more concealable for me than the 26; the 26 I carried AOWB in a Mitch Rosen Upper Limit I had for my G19; the 43X I used a JM CK (I think it was an AIWB 2.5 WC).
The 43X got traded for the aforementioned G48, which was almost the perfect carry gun, excepting IT would not run my carry ammo after I had the slide milled for a 407k. So I sold THAT for a 365X a few years ago and haven't looked back, not once.