PolarPro's are the "go to" but some people complain about the price. Personally I found them to be so cheap relative to the cost of the drone that it was a total non-issue, and I went with a product I was comfortable with, has good support, guaranteed gimbal compatibility, multi-coated surfaces, and a lifetime warranty. I'm sure other companies make good filters too but I went with the "safe" choice because there was no good reason not to (for me). There is no objective testing to look at regarding filter quality that I have seen anywhere, so I just picked based on the best available information to me at the time. I am extremely picky and I have been happy with them so far, YMMV.
Just a caution regarding polarized filters on drones, they are very difficult to use properly and effectively because your footage will change any time your angle to the sun changes. You need a very well planned out flight path to get much value out of polarizers. They can also completely eliminate certain things that you may want in your footage, such as rainbows or the colors of a sunset reflecting off other surfaces.