I have an Astronomik UHC-E and OIII. its Very nice! I cant comment on lumicon filters, I've never owned one.. but to my experience (somewhat limited experience) the Astronomik's are nice...
I own the Astronomik UHC, OIII and the DGM Optics NPB. I previously owned the Lumicon UHC and OIII. I have also used recent manufacture Lumicon UHC and OIII's which are different to the older versions, that I previously owned. I have also used the Televue OIII and Bandmate, the Meade and Celestron equivalents, the Thousand Oaks versions and the Orion Ultrablock and OIII.
Of all those I have used my preference is for the Astronomiks by a small margin over the Lumicons. The Astronomiks are made in Germany, the Lumicon is made in the far east. The mechanical and optical quality of the Astronomiks are excellent. They are also the most expensive.
I haven't used the Baader filters but have had good reports on them.
If you only wish to buy one filter the DGM Optics NPB is an excellent choice. It is a very narrowband UHC filter and is almost a hybrid UHC/OIII filter. It provides some benefit on the widest range of targets compared to any other DSO filter I have used.
If you did decide to buy the Astronomik UHC, which is an excellent filter I would recommend against buying the cheaper "E" version if your scope is over 10" aperture. The "E" version has a wider band pass than the standard Astronomik UHC filter, thus it is better suited to smaller aperture scopes. If your scope is under 8" aperture the "E" version is likely the better choice of the two, as it allows more background detail to show through. The Astronomik OIII is an absolutely outstanding filter in a large aperture scope. So it should be for nearly $350 in the 2" version.
The best way for you to decide is to get hold of the transmission curves for the filters and to compare things like how wide the band pass width is , how well they reject the undesireable wavelengths and how well and consistantly they transmit the in the bands they specify.
Other aspects to consider are how they are manufactured, price, and to read the threads here on filter selection and on other boards, and to take everything the sales people tell you with a grain of salt.
It also depends on how you plan to use them, visually ? as a front filter on a lens (if you can do that even ?) as a dropin in a camera body ? in the optical path of a telescope camera system ?
I assume you are expressing this opinion after having used all the contenders in different aperture telescopes on a wide variety of different types of targets? Not merely making an assumption on what you think might happen having read a few graphs and charts on a few websites. Also remember that most astronomy forums are US dominated number wise and Lumicon is a US product and some opinions may not necessarily reflect an unbiased performance assesment.
Having used them all in different scopes I can tell you the Lumicon are very good filters. They don't beat the Astronomiks by a long stretch.
I also use the Astronmik OIII (in a 10" newt and a 16" lightbridge) and find it great. The other thing I like is the coatings are very hard wearing. I've dropped the filter in the dirt, just rinsed it off and given it a buff with a lens cloth and it was like new.
Astronomik state on their site that unless you have silicone carbide (from mirror grinding) there is hardly a chase you will scratch their filters.
I do intend to buy a UHC filter for viewing from home and this will also be an Astronomik, so you'd have to say I'm happy.
I can't comment on other manufacturer's filters as I haven't used them.
Hi ,
Just a quick note to table my experience with comparison between the Lumicon and Astronomic UHC filters. I spent many hours swapping out both filters a number of years ago at The QLD Astrofest. With out a doubt the Astronomic UHC filter won the contest with a noticeable improvement in the brightness and contrast of bright neb and planetry neb. viewed.Some time was spent on IC 5148 in Grus thru a 20" dob. There was no doubt which one won. UHC again..
Cheers Zub
I bought and sold here one of the older lumicon uhc filters some time back .
Despite the stated transmission curves of later offerings being alot better to look at on paper .. my old filter in hindsight
( I've gone the 2" route ) ..did a better /differant job than the newer ones I've seen for my eyes
and I have no idea why ?
I've had the opportunity of "testing" various filters with my spectroscope ( similar to Buil's tests) and find that the leakage of Hb into some OIII filters ( these emmision lines are very close together) can help visual observers of planetary nebulae. A good Light pollution filter is a better long term buy, in my opinion than very narrow filters which are really only used by DSO observers with Mono cameras.
My 2c
I found the Astronomik 1.25" UHC-E when used with my 10" Saxon dob to give excellent results especially on bright nebulae....the other filter is a 1.25" Sirius Optics Contrast Enhancement filter...brilliant for star clusters etc.
..did a better /differant job than the newer ones I've seen for my eyes 
