I've been very happy with the B+W XS-Pro Clear MRC-Nano filters. They're expensive, but I don't see any IQ loss under normal circumstances and they add just a tiny bit of flair under very difficult lighting. If you can, test for flair problems with whatever filters you are considering.
If anyone points you to the lenstip UV filter comparison keep in mind that digital cameras don't benefit from UV filtering.
edit: I use these filters on the 70-300G, 70-400G, zeiss 85mm, and zeiss 135mm.
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