Generally 2.0 is considered the respectful default option, if you're just using public trackers with no ratio requirements.

Personally, I look at the torrent's overall health.

If it's a super active torrent with hundreds of seeders I'll set it to 1.5 or even 1.0 and auto remove when done to save resources on my homelab server. Sometimes with high seeder counts it can take ages to even hit 1.0. They all get automatically moved to a completed folder when done so I can pick through them and categorize them.

If its a less active torrent I'll choose 2.0 or 3.0.

If it's a super rare torrent with less than three seeders, which there's sure a lot of, I'll set it to infinite to keep it alive. I've gotten some smaller torrents up to a 30+ share ratio.