I vote "none" as well. Your plumbing should be set up so that only a very small amount of water can ever drain back into the sump when the return is shut off.
In 15+ years of reefing, I've only ever seen once instance where a check valve made sense.
I used a Spears True Union Check valve on my tank and it failed the very first time I shut off my pump. Don’t bother. Just plan to have your sump large enough to contain the additional water.
I agree, size your sump to contain additional water. If you absolutely require one then a Y check valve that can be easily cleaned/serviced would be the best option IMO, though more costly.