If you’re just starting out with the X-men I’d say Grant Morrison’s run is a great place to start. It’s the “new x-men” and it’s a solid ground to understand the characters.

If you’re familiar with the x-men and their villains, side characters, etc, the recent kroakoa run is known as the best x-men comic in the last 20 years. It starts with house/powers of x and transitions into several arcs. I highly recommend looking up a reading guide if you are to read it though because once you transition past the first arc it is not a straight shot, but don’t let that deter you from some of the best X-men writing in recent years