The way I use it personally is basically playing 2D classics with FBNeo and a few 3D of the era I go with mame, as obviously, FBN never intended to emulate 3D graphics as far as I know, but there are still a few obscure 2D games that FBNeo doesn’t run, these are less known games, though.
Reasons being, FBN feels lighter on the resources and starts faster, it aims to emulate only 2D arcade games (albeit it also emulates consoles, but I wouldn’t use it for this goal if I can opt for dedicated cores).
It supports runahead and similar input delay features, among other retroarch options that feel better integrated.
For vertical games, I have better luck with mame, it just doesn’t behave right with me when I set vertical mode in FBN for some reason.
Mame is great but it’s goal is way too big for the average player.
While I feel that FBN could also benefit from having a FBN Pure variant that would emulate only arcade games.
It’s true that many devices can handle the extra load with relative ease, but the lighter, more focused variants would provide a better experience overall.
All in all, I was never disappointed with either and we can only be grateful for having two great choices to play with.
