Personally, I never carry handhelds in pocket as well, but I do always consider their pocketability factor - it is more of "if I need to, can I ?" and "how fast can I whip it out, and put it back?"...so to speak.

The size does matter but having a built in protection of the screens is just as important. Only clamshell designs are pocketable imo. And pretty much only GBS SP is it size wise. All others go into my backpack or a separate own case or bag for the console. Sadly the SP are to my hands not nice to hold and play on. Would give the victory to the DS lite. It is small enough to get a pass, can share pocket with other stuff with low risk of damaging the screen and is more comfortable to hold and use. And the battery life is awesome.

I'd even argue the Switch, Switch OLED and Switch 2 are to big for a handheld generally. They are to heavy and not comfortable for longer playing sessions. PSP is probably my sweet spot for handheld size when using it.

Clamshell is my go to as well - I'm not so specific for the size, since I have no problem with AYN Thor or Retroid Pocket Duo sizes, since I don't actually carry handhelds in pocket, but those can actually be carried around in jacket without risk of damaging the screen.

I would love to see Nintendo release 6" screen Switch 2 Lite as a clamshell, even if its without second screen, a la Retroid Flip, and have actual pocketable handheld offering that way.

Vita is probably as far as I go, or may even be too big for my liking. I like my gaming handhelds to be able to fit in my front pants pocket without sticking out.

Best handheld size for me was the GBA SP, NDS Light and PSP Go. PSP Go was my perfect device as it was very comfortable to also be used as a media and MP3 player before we had smartphones.

Picking up the AYN Thor so I'm excited to give that a try.

Yeah, Thor is really great, and no wonder so many people are getting it, though I find Pocket Duo to have better layout if DS/3DS emulation is primary goal. That said, Thor's SoC is quite a bit better.