It doesn’t really matter for gaming at the moment. Might make a big difference in the future when GPUs can talk to PCIe SSDs directly, but that’s 1-2 years away in practice.
The loading time tends to differ less than 1 second between a SATA SSD and the best NVMe M.2 SSDs.
The Kingston A2000 is a nice budget option. Samsung 980 EVO/PRO is a good performance option, but for gaming specifically it’s currently a waste of money.