Wider channel and flatter seat is probably the bates. Of the three, stubben might be the highest quality but it’s the last one I personally would choose. I’ve never sat in a stubben i really liked, including the high end bio seat versions.
When I’m saddle shopping, or even just researching, I set myself up a variety of ebay search notifications to send me every saddle coming up that I think I might want to look at, which for me will include both brand specific and non non brand specific searches. Include high end saddles you think will be out of your budget. For under 800, I have purchased albions, counties, kieffers, pariani, bates; the beautiful modern arc de triomphe was 900.
In the meantime, sit in any saddle you can just to get a read on what you like.
You don’t mention, do you like the pessoa? Because those do come in different tree widths and configurations and you can get a lot of them for under 1000.