[wanderer2]

Which filter brand is considered better/best? Hoya, Tiffen, etc.

You can find some useful info on this subject on lenstip.com, especially oh polarizers.

[zapp]

Here are the most neutral ND filters in my opinion.

- Breakthrough Photography
- NISI
- Wine Country Camera

To be honest I think Nisi is on the same level as Breakthrough Photography and the Wine Country Camera are the only ones that they tested their filters on 100Mpx medium format camera.
I guess that you will have many answers as many people prefer something else... Personally I set my mind to get Wine Country Camera filters but do not rush as I have other things to finish first.

EDIT: I did not include Lee filters as they have a bit of blue cast in my opinion. Had them checked for few weeks and gave them back.

I can test any fiter for you on 100 Mpix camera. Would it increase the value of my filter?

[RAART]

I can test any fiter for you on 100 Mpix camera. Would it increase the value of my filter?

Higher resolution cameras will reveal the imperfection in glass used and this will show the difference between the filters, assuming they are tested under the same conditions. Unless you are manufacturing those filters the test will nor decrease or increase the value but you will find out which ones are more suitable for your application. Also the test results if they are published they are accessible to broader audience can affect the value of the filters off course...

[angerdan]

Which filter brand is considered better/best? Hoya, Tiffen, etc.

A good UV filter (leading brand, multicoated) does cost at least $15, depending on the filter diameter.
Well known brands delivering good quality are:

• B+W (F-PRO, XS-PRO)
• Heliopan (PMC, SH-PMC)
• Hoya (HD, HD3, HD nano, FUSION)
• Kenko (Pro1 digital, Realpro, Zéta, Zéta EX, Celeste)
• Marumi (DHG, DHG Super)
• Rodenstock (HR Digital, HR Digital pro)
• Tokina (Pro Lens Guard, Hydrophilic)

Nothing more to say about this besides the reviews and tests:
filterzone
UV and Clear Lens Protection Filters Review
HOYA HD Protector Filter Review
Lens Rentals | Blog

Many things can be measired, especially in optics. FIlters can be categorized by glass quality (thickness, hardness), coating quality (transmission, reflectance) and coating surface features (like anti-stain, anti-static, hydrophilic/water&oil-repellent).