Santa has been good. Fooled him again! Anyway, need some advice as usual from the knowledgeable shutter bugs. I have $180 to spend. Pondering getting some additional items for the Sigma 150-600mm lens; takes 95mm. UV, polarizing, neutral or what? I plan on doing a lot of wildlife photos this coming year. I went to B&H and found some listed around $40 with 5 star reviews. I know the Canon brand will be more expensive for one item and would be willing to buy the Canon even if it takes more money. Thanks.
Either a circular polarizer (CP) or neutral density (ND) filter would probably be the most useful to you. I wouldn't both with any UV filter. If you need simple protection for the front element, I recommend using a high quality clear filter.
Personally, I use B+W filters (their XS-Pro line). No color shifts, their CP has minimal light loss, and the brass construction helps prevent binding (since most lenses wouldn't have brass filter threads).
For ND, I use 3, 6 and 10-stop (all fixed; I personally do not like variable NDs). If you plan on doing long-exposures, these are very useful. But I also use them when using off-camera flash (to avoid having to be in high-speed sync).
I agree with the opinion that you do not need a UV filter, because there is already a UV filter layer built into the digital image sensor assembly. I only use a Clear filter, to keep the front element clean. I do not use one for protection from bumps and bangs.
Using lens filters is a hot button topic. Setting aside the “lens protection” argument for a moment, there is also the opinion that filters degrade the image. Yes, a cheap filter can degrade the image.
Then there are purists who do not want any filter, because the feel it degrades the image. I do not feel high quality filters significantly degrade the image, but I do feel that come can compromise the camera’s ability to focus. One the rare occasion when I might use an ND filter, I am using a tripod and I lock focus without the filter. I add the filter, and then take the shot.
You don't need any filter(s). Spend that money of a Black Rapid strap.
The only filter that makes any sense, or even cents, is a polarizer. And, it makes very little to boot. Learn PSE which is free to do and will do most of what that filter stuff does only better than the actual filter does.
I put protecto filters on almost every lens I own or have owned. But I do not use them on my big super tele lenses.