Hi Craig,
I own the Astronimks OIII and UHC filters and the DGM optics NPB filter.
If you only plan to buy one filter the DGM NPB may be your best choice. It isn't expensive and works on a wider range of targets than the UHC and OIII filters individually. It is a very narrow pass band UHC filter and essentially is almost a hybrid UHC/OIII filter. It is also idealy suited to a scope of 12" aperture.
http://www.omegafiltersebuyer.com/se...ers/Categories
http://www.cloudynights.com/item.php?item_id=1578
Cheers,
John B