That depends what games you plan to boot up. Are they the 100+GB Legendary Edition types with all the DLCs, or are they <15GB indies? If you think it could be the former now or in the future, I wouldn't get less than 512GB (also, keep in mind that games are only getting bigger). You'll run out of storage on the 256 faster than you think, either way, and if you're trying to save money, there's usually deep discounts around Christmas.
I always recommend Crucial drives, as they have been solid choices for me (I have an older MX100 that's still going strong 10 years later). What kind of interface do you have? SATA? NVME?