I have 3 drives in my pc. I have btrfs for root so I can do my snapshots, and the rest are on ext4. I've heard very good things about xfs, too, but I'm more familiar with btrfs and ext4
I absolutely love my set up. The non root drives are strictly read only since they're mostly to save my games and personal data. Data doesn't really move around much there, so ext4 is working perfectly for me.