Alright a few things for this:
1. Shape of your hand compared to ergonomics of the mouse. Find what suites your hand better
2. Software. CUE software is bad, that keeps me away from corsair products in general, although the keyboards are really nice. It's clunky and not very intuitive. Logitech G software is okay at best, but personally I Think it's league's better for mice.
3. Size of the mouse. G300s is a slightly smaller fit mouse. The other is closer to average.
4. Preference. What you feel best with, what keeps you consistent. As a CS player practice, reliability, and most of consistency is what is most important. I personally use the g300s because of how I decided to pick a cheap mouse.
Pick what you think should be best for you, and don't be afraid to return a mouse either.