I find the house mates that mumble a lot harder to understand than those with thick accents.
Rodrigo has a very pronounced accent and yet I never have a bother understanding him, Siavash's accent is a lot closer to
received pronunciation but as he mumbles a lot I do find myself needing the subtitles they give him. David, Lisa, Karly, Sree and Charlie may all have more obvious accents, but I never need subs to understand them.