For me (only 2 experiences with 2 different bulls), I enjoyed a lot:
 - watching them while masturbating,
 - filming everything (GoPro for a continuous large angle of the whole evenings and iPhone to make many small movie with different angles),
 - watching on my phone live (thanks to the GoPro I installed) and masturbating at the same time - I was on the bed - my wife and her bull going alone in the bathroom and having sex in the shower,
 - receiving blowjobs from my wife while she was pounded hard,
 - licking her clitoris while the bull was fucking her (but complicated as she was moving a lot, next time we'll find a better position for this),
 - watching her being able to take a 9 inches cock fucking her ballsdeep really hard while she was kissing him passionately and grabbing his butt for him to take her even deeper,
 - watching the second bull fucking her bareback and cuming inside her and then pushing back inside with my cock the cum leaking and fucking her gaping pussy (cum is the best lube),
- my wife being a pornstar and loving being treated like a fucktoy by them.