Nebula filter question ??

Probably been asked and answered here before, but I missed out. What is the "hands down" best filter choice for accentuating the nebulosity from the background? I have tried a "sky glow" and seemed too dark for my aperture (9.25" SCT) using a 26 T5 EP... I have heard of an OIII not sure what that is, and the UHC filter,also a LPR ?? any guidance in the right direction would be appreciated, John M

John,
The O-III passes a very narrow band of the spectrum. Also referred to as a "line" filter, because of the narrowness of the band-pass. Good for planetaries, supernove remnants, and many emission nebulas. Maybe too dark for smaller apertures.
The UHC passes a wider portion of the spectrum, but still rather narrow, hence it is sometimes called a "narrow band" filter. Probably shows more emission nebulas to better effect than the O-III. A noticable difference between the two filters is that the O-III will show a darker background sky, and extinguish more stars, than the UHC. The UHC will probably work better in smaller apertures than the O-III.
"LPR" stands for Light Pollution Reduction, which both of these filters are.
I'm surprised that you would find the Skyglow too dark in a 9.25, as it passes the widest portion of the spectrum of all three filters.
If I had to choose between the three, I think I would select the UHC. I expect that it will perform more effectively on a larger number of objects.
Hope that helps!