Magnification comes down to the size of the target you want to hit and the distance. I’d estimate that 10x would get you a usable sight picture on a 2 moa target at any range. Myself, I’d want more if I were going to be engaging targets that small. Lotsa matches are roughly 2 moa targets, and I shoot mostly at 17-20x.

I’m pretty comfortable on a man sized target out to 700-800 with 8x.

One thing not always mentioned is that higher magnification allows you to spot impacts (hits or misses) much more effectively. Can’t shoot in the wind very well if you can’t see where the bullet hit.

Decide what your precision requirements are and buy accordingly.

To repeat the excellent question above, what’s your budget?