I would say Mubi. I had BFI for a bit and actually found it quite limited. The player was also rubbish for.me but I have an old laptop so it may not be an issue.
I find Mubi has a really wide range of films, good retrospective and themes and as @Aggpass mentions, the 30 day window gives you extra impetus to watch things.
Mubi also has an archive where you can rent films not showing on the main player