When you get the server or slot most of them let you install whatever software you want like rTorrent or Deluge. Dont forget because the
seedbox is usually located overseas etc you have to access it via a WebUI or you can set up your torrent client to act as a "thin client" ie it mirrors what the
seedbox is showing.
Most
seedbox providers offer 100mbit and 1000mbit (1gbp) plans. Usually hard drive space is lessened if you want the quicker line.
take a look at whatbox.ca, feralhosting.com and varsbox.com for examples of reasonably cheap and easy to use seedboxes