I don't really have a specific favourite, it's more of a favourite species, it's literally any symbiote. There's something I find really interesting about the symbiote, the way they can bring out the worst in any creature makes for really interesting stories.
#1) Harry Osborn’s Green Goblin - there is something epic about your best friend also being your mentally unstable worst enemy that can snap at any moment.
Peter has several of these tragic foes that are close to him but mentally unstable. Norman and Harry as the Green Goblin, Lilly Hollister as Menace, Dr. Conners as the Lizard.....I’m sure there are more that are just on the top of my tongue. I think it adds to his level and weight of responsibility and of the moral and emotional concept of the storytelling.