Do not use Tixati or uTorrent or Bittorrent. these are proprietary software.

Deluge, QBittorrent, rTorrent, and Transmission are all fine options and I think they each excel in different ways. Most seedboxes use Deluge or rTorrent.

I never really like QBittorrent because I don't like the libQT interface. It's probably fine to use.

Deluge is the preferred client by seedboxers who seed new torrents. For torrents that are less than 48 hours old, deluge seeds much more than any other torrent client. Deluge also downloads more aggressively than the other clients. The drawback of Deluge is that it loses performance at around 500 active torrents.

I haven't noticed Transmission being offered by most seedbox companies for use. It is a fine client. In my own experience, it is limited to around 2000 active torrents seeding before it loses performance. I've known people who seed more than 2000 torrents and they run multiple instances of transmission with different torrents seeding in each.

rTorrent is the best in terms of long term seeding. It is the most lightweight out of the clients. I've has up to 6000 torrents active seeding in an rTorrent client. I would guess that it fails somewhere around 10000 active torrents. The web interface will fail long before it reaches this point so you have to figure out how to control it by command line.