Hi Erik;
I have just been going thru this so will be interested to see any other responses but from my limited understanding, with a colour ccd such as you and I have, the LPF or UHC seems to be the best all-round for improving contrast on emission nebulae. A good link showing the spectrum transmitted by several types is at
http://www.astrosurf.com/buil/filters/curves.htm and the Astronomik UHC, Lumicon Deep Sky and Baader UHC-S seem to have the best balance for blocking extraneous streetlights, skyglow, etc. while still transmitting the really important bandwidths. I bought the Baader UHC-S because I could not easily locate the Lumicon and Astronomik do not suggest theirs for a low f-ratio (I have a Hyperstar at f2). Not so much use for galaxies I believe or for reflection nebulae. Hope this helps (and is mostly correct
).