The team I was using at the time wasn't strong enough to run Expert, so I just ran Standard about 10 times or so to use up my Stamina on level-ups. I got a gold chest with a Tail in it every single time.
That's not a lock by any means and I'd probably still run Expert if I could, but it definitely isn't a bad way to go if that's what you've got available.
Remember though that they'll probably run the SP version of the event Sunday again with super-increased drops, so that'd be the spot to plan around.