So you can have any villain or antagonist at your service to protect you. But their heroic opposite is gonna try and kill you. So who do you choose, weighing how powerful they are vs. how powerful the hero is?
So for this I'd pick S2 Discord. All he needs to do is hide the elements better and the mane 6 wouldn't kill me. And even if they did get them, we could just travel to other dimensions. He's basically Q if Q were actually a villain.
Your turn.