Video, best?

If you're talking about companions, Motaro is the strongest because some abilities don't affect him. Shao Kahn isn't difficult to defeat. If you're talking about players, it depends on how well they play that character. So, you can lose to anyone if the player knows how to play them. It's easy to defeat the bot with Cyrax using the net, but that won't work against a player. As for Sector's rocket, it doesn't hurt if the player is attacking Sector at the same time. Not always, but it happens.