openSUSE is available via ftp/http or BitTorrent. The Mini CD for network installation is only vailable via ftp/http.
Using BitTorrent is recommended, especially when downloading one the DVD image. BitTorrent downloads have several benefits, the clients protect against data corruption and you help relieving the load on the servers by participating in the upload - if enough people participate it will also be faster than the centralized servers - for everybody. Whatsmore, it allows you to stop the download at any time and resume it later. More informarmation is available at BitTorrent and openSUSE.
When downloading images other than the Mini CD images, it is strongly recommended to use a proper download manager to reduce the risk of corrupted data.