[dsport]

No filter is the best.
However, I am living in a crowded city with air pollution most of the time. So I would always protect my lens with UV filters. I would not like to risk my front glass elements especially most of my lens are A*/FA*/LE/DA*. However, I am lucky enough that all my UV filters are original Pentax SMC filters except FA31mm whilst using B+W MRC.
In my environment, my opinion is for cheap lens, you may skip the UV. For expensive gems, UV always for protection. But one should use a high quality brand such as B+W, Hoya Super HMC, etc. However using a high quality brand doesn't guarantee you won't encounter any flare at all, it would only mininize the chance of occurence.
I have the experience of using DA*16-50mm with Hoya HMC Digital Pro UV, still encounters a flare against the sun in one pic and I am sure that such flare is caused by the filter.
Needness to say, best to take off any UV for indoor photos if the environment permits you to do so without risking your lens.

[Clicker]

I only have the kit lense and the 55-200 cheapos since entering the Pentax realm compared to most of you guys, seeing this thread before i got my kit i decided to go sans filter but all my prior/current systems have filters (UV) as protection. I've only had one mishap where the filter (B&W) was the only thing damaged/broken when i dropped my bag with two full Mamiya 6 systems off a ledge everything else was fine but that one filter
I will put filters on the more expensive lenses i acquire in the future though.

[rogerstg]

Unnecessary precaution for a rampant paranoia of damage to personal property.

+1. I think many folks could buy another nice lens with all the money they've spent on high quality "protection" filters.

And if they haven't bought high quality filters they'd have saved money by buying lesser lenses because that's effectively what they end up with by pairing quality glass with a crap filter.

[rburgoss]

I use to have UV filters on all my glass, but since switching to digital and doing a fair amount of night shots, all the filters came off since they produced ghost images from highlights.

But then, now that my wife is getting into photography, with my ist-D (since I purchased my K20D a couple of months ago)... well, its almost unbelieable, that she manages to leave FINGERPRINTS on the front elements of every single lens she plays with. Of course, filters are on again and I just remove them for night photos.

Robert

[Gooshin]

ohh noes, finger prints!

[Bophoto]

I have seen test in 2 different magazins in Sweden, "Foto" are use Hasselblads test eqipment to test only optics, not through the camera, the other magazin "Kamera&Bild" just look at pics. The test indicats(as i remember) that sharpness/contrast are not affects of good glasfilter.

However then you take a photo with sun or other sharp light in picture, you add an extra glas to the lens and the filter is out in front of lens for the sun to shine on(producing ghost). I use filters on most of my lenses, but not on Tamron 90 macro, just because of that.

Now Pentax have SP coating on DA lenses, so i think the problem with scratches isn´t so big, in future we probably have glas that are harder than betong in lenses...

UV and skylight 1b don´t do any extra exposure for your camera, but skylight 1a does.
Kenko pro and Soligor high (something) have probably same coating as Hoya super, but are cheaper.

And thy are filter expensive? you pay for the name, and also try to buy all parts of a hole lens, and you have to pay dubble or more for the lens. and if Hoya sold bigpack of UV filters, the price was...