It'll depend on your workloads. If you're GPU render some complex 3D scenes for example, that have a lot of polys or high-res textures, you might need more VRAM.
I regularly go beyond 8GB on some of my GPUs, and 11GB on a 2080Ti is much better. If you think your scenes are relatively simple, then the 10G version should suffice.
You can run a test, render one of your typical scenes (maybe on a friend's PC) and see how much VRAM you're filling up.