It's a tough decision choosing between WBSS and Jam because they're both strong openings to the show. I couldn't choose the HIStory medley from that tour because while it's also a strong opening after the amazing video intro and coming out of the spaceship I don't think it's as strong as the other two openings.
With that being said,I do think WBSS as an opener is electrifying and it was a great way to get the audience fired up and on their feet ready for the show ahead of them. The Bad Tour opening was unbelievable with the intro,especially seeing the one with the feet (as already mentioned by PoP). The intro was just so atmospheric and really got you pumped for what would happen once the screen was lowered revealing Michael and the dancers.