Canon-divergent AUs are my favorites too :) And I think time travel is related to that?, because it's often basically canon-divergence "what if they had additional information (and sometimes powers etc.)"
I also really like "add a sprinkle of magic" AUs, e.g. everything is the same but one character has magic/is a werewolf/lives with a ghost etc.
Mundane coffee shop AUs are in general my least favorite, but even they can be very good in the hands of a good writer.