All slot machines online are different, they are set by something called variance, they can be high variance and low variance, what this means is a high variance slot pays poorly for long periods then hits big and low variance means it pays smaller wins more consistantly and medium variance is somewhere in the middle as you could have guessed.
The point in having Low variance slots is for a casino to always win in the long run and you need to avoid these machines.
Luckily Microgaming only has a few of these machines which i have listed below but also as most machines are just skins of other slots, dont play slots that look very similar to the ones listed below, you will understand what i mean when you play slots enough..
The Slots to avoid at Microgaming casinos
The slots to avoid at Playtech Casinos