My personal choice for any R2R is to avoid oversampling, otherwise I would use delta-sigma. So, for me personally it is NOS mode, meaning no filter or hdr.
HDR makes sense in OS mode and again it is hardly a noticeable difference.
All OS filters have their own sound signature, it's up to one's personal preference. I would use the one that is closest to the digitalized source which is (named differently in different devices) fast normal/sharp. But again, I personally would not use any filter with R2R.