I have Ha filters in 7nm, 6nm, and 3nm. I think the contrast the 3nm provides and its ability to cut everything out. I think if I were to go back knowing what I know now that a 5nm is probably a good mix between the two. It will assist with the full moon and bright locations better than the 8nm would. The 3nm is the ultimate light pollution filter however and I have been able to image in the middle of down town under a street light without issue.
If budget isn't a constraint a 3nm is without a doubt the way to go. But if its a little tighter a 5nm and 6nm would be the way to go. The 8nm would be fine but having that tighter bandpass would be better for contrast.
Edited by skyward_eyes, 08 November 2019 - 01:39 PM.