Which seedbox providers would you recommend?

ultra.cc user here as well. Cheapest option (no streaming) and am super happy. Yes, it's not a dedicated connection but it is sufficiently fast. Shell access to the box, easy app installers, webdav, sftp, and web access. Egress over ssh (rsync/rclone) does not count towards bandwidth (unlike http(s)) Been using them for 6 months now.