To be more specific, in regards to Saturn games, does ISO-MP3 provide decent quality rips? How big of a difference is there between the two formats? Also, the only difference in quality would be the audio right? Would people prefer BIN-CUE rips over ISO-MP3?
The only substantial advantage provided by ISO/MP3 is that the resulting image is smaller. ISO/MP3 is slightly more difficult to work with and consistently creating a disc layout identical to the original is nearly impossible. Fortunately, most Saturn and Sega CD games don't really care which sector each track starts at, they just read from wherever the track happens to be.
BIN has a couple of notable advantages and one big disadvantage. It is usually more straightforward to burn and provides a copy closer to the original, but it tends to be bigger, particularly on games that have a lot of audio. For games that store all their audio on the data track, or create it with synthesis, MP3 will not provide a significant size advantage. In any case, a bigger image takes up more space on FTP sites and takes longer to download.
It's worth noting that cuesheets are not format-specific, and it's a good idea to include a cuesheet with ISO/MP3 rips to ensure that the resulting copies are as close to the original as is possible with MP3. This also helps eliminate some of the confusion that can arise when attempting to burn ISO/MP3 images.
Usually the audio quality is the only difference. However some games are very picky about post gaps and pregaps and a bin/cue rip makes this much easier. Also dual data mode discs tend to be easier to burn as bin/cue.
Which do people prefer? There's a whole spectrum of opinion out there.