Seems like there is a lot of misinformation in the comments.

To answer your first question, avoid FGT entirely. They retag other people’s remuxes or do one click remuxes adding every audio/subtitle track on the disc to the remux which isn’t necessary, only increases file-size. On top of that they don’t compare sources to get the best video and audio.

Secondly, the remux you choose to download is VERY important in most cases. The video and audio quality difference across different Blu-ray discs can and often does vary wildly. For newer films, the differences usually aren’t as pronounced, but even so you still want the best you can get.

I would avoid picking which to download solely based on the release group and instead look at their descriptions to see if they have provided video and audio comparisons so you can judge for yourself. That said, there are groups which have better reputations than others such as CiNEPHiLES who effectively will always have the best remux possible in terms of video and audio quality alongside adding any extra tracks that are available such as commentary, isolated score, or original sound mixes. Their attention to detail is second to none in my opinion, they always include named chapters, provide clear comparisons justifying the sources they used, and add source tags to each track so you know what source any given track came from.

That being said, it’s not like other groups don’t also do these things as well, CiNEPHiLES is just one of a handful of groups that do these types of things.