Amphetamine[0] works pretty well for me. They also have an extension (a kext, I think) that gives it more reliability. I don't know how reliable it is without that extension though.
I've been using the more bare-bones KeepingYouAwake[0] just because I came across Caffeine first and this was suggested as the continuation of that simple utility. The icon makes it obvious whether it is enabled or disabled
Edit: I see now that Amphetamine has the option of a similar-looking icon to make it more obvious whether it is enabled or not
I used Caffeine for years and never really thought about it much, it's always been useful. But I installed Amphetamine lately on a new MBP and I've used the schedule and countdown modes multiple times now. It's a great tool and the added functionality is useful.
Edit: I see now that Amphetamine has the option of a similar-looking icon to make it more obvious whether it is enabled or not
[0] https://github.com/newmarcel/KeepingYouAwake
(My first HN comment, via Orion Browser)