Its up to you.
Generally, single coils use 250k pots and humbuckers use 500k.
The higher the value of the pot, the more brightness it lets thru when full on, or the less load it has on the circuit when its full on. Hence, being that single coils are bright, ppl generally don't want it to break glass, so its 250k. And humbuckers, being warm, usually go with 500k to let a tad more brightness thru.