To the best of my knowledge; all bar adaptive are streamed via RB. Could = already in your RB account. Torrent= scraped from a torrent site, then downloaded to RD (or most of the time already in RD cache). You stream from RD. Hoster: direct from a web hoster and streamed via RD (personally I find these of little use). Adaptive= I believe this is only if you have legit services linked (e.g. netflix). I don’t believe it’s been implemented yet although I may have missed it. Hope this helps.
Ask far as I know (I’m a user not a dev), it shouldn’t make a difference as all come via RD, so the speed or buffering will be dependent on your internet connection and connection to RD servers.
I personally turn off hosters and scarpe only one torrent site (torrentio) as it’s super fast and gets enough links). But I use fen primarily, with Seren as a back up.
I have fairly slow internet and never have any buffering issues. I would suggest looking into your video cache setting (Google Kodi advanced XML settings link to Kodi guide) or set Seren to select only smaller file sizes.