Both phones can currently be picked up with up to $130 savings, but there is no word on exactly how long the promotions are going to last, so you better act quickly. B&H seems to have the best deals on the Nexus 5X, with prices all the way down to $250. The 32GB Black one seems a particularly good bargain at $269.
And if you would rather go for a Huawei Nexus 6P, then you are really spoiled for choice. Best Buy has you covered if you are in the US and prefer local pickup.
Amazon is also on board with the promotions and can't really be beaten in terms of shipping services.
And last but not least, Newegg is also an option, especially if you enjoy freebies as the Nexus 6P comes with a $25 gift card, selfie stick and case.