cnckitchen did a pretty good comparison of different gitd filaments. There's a video on their channel too.
I don't remember if the comparison covered this, but I would expect PETg to work better than PLA for gitd stuff because it's inherently more transparent, right?
I should have 3 different glow filaments somewhere, one PETG, two PLA. Typically I preferred the PLA versions - they had a bit more uniform glow. The PETG one had brighter spots, but as it was mostly transparent individual spots were more visible than with the PLA prints.
Nothing glow-in-the-dark is anything that could be described as "bright." What you probably want is something that is florescent under a blacklight. Someone probably makes something specifically for that, but otherwise, a lot of dyes are naturally florescent
The Polymaker neon filaments fluoresce under black light. Someone was posting pictures on the Voron discord of their printer with the parts all printed in polymaker's neon abs and under a black light it looks like a 90s arcade. It's beautiful.
If it’s colored, it’s bad. I have a lovely purple GITD pla that even had a warning about the purple one not being that much glowy, it still surprised me. Very short time, very dim even if charged with a UV light… I like the color so all in all no big deal, but wow. Speaking of the suggestion of using UV reactive filament (light that, by the way, would keep the GITD ones glowing) some colors just look bright even without needing to be special. For example I have a bright green PETG that pops with UV light.