Whats "best" is what is best for the DOG, not what feels best to the human!
Most dogs do not like anal. In most cases they are forced, at least initially, and conditioned over time to tolerate it, which is the more subtle form of rape and should always be condemned. There are cases where dogs show obvious interest in being anally penetrated without being coorced and conditioned, but those cases seem to be in the minority.
Most videos glorifying anal penetration of dogs are edited in a cerain way to not show the whole dog and the whole act from the beginning so the body language of the dog isnt fully apparent which makes it real easy to make rape look harmless. Combine that with the dog having been previously masturbated and maintaining that erection during penetration (despite being penetrated not because of it), that just adds to the illusion.