Day to day pocket light use, 14500 or 18350. A few 16340's. Bump-in-the-night or dog walking, 18650's. Zombie lights? 123 or AA lithium primaries. Rcr's are energy dense, easily topped off, and easy to find. Lithium primaries don't normally leak, and store for years. 👍
18650 all the way. Plenty of charge for day-to-day use even on IMRs with lower capacity (especially for me, as I rarely use a mode past Medium [10-15% of max]), so if I get stranded in any kind of situation where I need light for an extended period, battery life is not a concern. And nowadays they're pretty easy to find and buy.
I pocket carry a 14500 light and a AAA light daily. When I carry a third light in a jacket or in my back pocket, it's a choice between 18650 or 2x18500 depending on the output required.
I prefer the form factor of 14500 as my primary light in the 80-100 lumens range, and a low power AAA at 15-20 lumens is perfect for a mouth-hold for shorter-term tasks or clipped to a hat brim for longer-term tasks. The 14500 is long enough to fit well in the hand but short and slim enough for comfortable pocket carry.
The third light option is for "tactical" or dog-walking duties.
Not an option if one is in the middle of their night shift. With primaries, you can instantly get back in business. Though with rechargeables, I always carry a spare set in my work-bag or sling-bag that are fully charged and ready to go.