All the selected games for the slot contest provide the opportunity win more than 1000x, so you can choose one of them and if you are familiar with the selected games then you should know which game that has better chance to give higher multiplier among the other games.
My only suggestion is to avoid the Reactoonz game by Play n Go, it is a nice game with possible more than 4500x max multiplier but as long as my experienced, this game is rarely give more than 1000x.
If I'm still actively gambling like few years ago, I will choose to play RIP City, Gates of Olympus and Sugar Rush.