A suggestion for you if you are participating in slot multiplier contest, try to find some slots where there is a chance to hit big multiplier in both normal spins and free spins.
This is very good advice!
If I'm not mistaken, the chances of hitting high multipliers in the base game (without triggering or buying the bonus round) are usually higher on high-volatility slots. So, you need to play those types of games if you are participating in the multiplier contest.
Also, the chances of winning big increase when playing slots that have a retrigger feature (which allows you to extend the bonus round) and games that have sticky wilds.
That’s my opinion based on my own experience, though.