A WF with no second indicator, HR indicator, and step counter will be the best bet. The screen dow not use power to stay on. But does use power to update. So by eliminating those three items it's now updating every minute. However the screen really does not use that much power at all. To really extend battery life turn off the backlight, HR, pulse sensor and GPS. Those are the big battery users.
go for simplest watch.. that doesn't ask for permissions.. secondly choose the one with less refreshes required... my experience shows Garmin default watch faces specially the digital ones are good
