nvme ssds are nearly reaching price parity with sata ssds. so if you can afford/if your board supports nvme, just get it.
corsair mp510 is the best value, in price and in performance nvme ssd around currently (obviously not from ocuk - overpriced as usual when compared to other etailers)
i wouldn't touch the QLC nand drives (ie crucial p1 or intel 660p) - unless solely for static mass storage with minimal writes.
what is your budget?
can't really recommend getting smaller than a 500 gb class ssd these days. much less pairing a 250gb ssd with a hdd for games! that's the worst combination ever.
the lag spikes from texture loads/load times on a hdd when gaming would make me jump off a building and commit suicide.
corsair mp510 480gb - £69 (not from OCUK)