In yesterday's episode of "Frederico Talks watches", his watchmaker Hans (purportedly former Technical Director of VC) said that if given a choice between ETA and Sellita, he would choose ETA every time and by a long shot. He explained that this opinion is based on the fact that Sellitas have higher rates of defects and that while the movements look identical to the untrained eye, that several components have been altered for cost savings purposes, which (according to him) contributes to the higher rates of issues on watches using Sellita movements.
I personally find this an interesting topic, particularly because some of the better known names in the industry (like IWC) have started using Sellita movements in their watches. In IWC's case, this means that watches staring at 4k new are sporting movements that 3rd party watchmakers consider inferior to the original ETA movements. I was already determined not to buy a watch with Sellita movement previously, but this cemented my skepticism towards Sellita movements.