While I have mainly used Namecheap (and like their attractive pricing on many TLDs, as well as their user system that to me seems very clear, logical and easy to use. I like the Namecheap Marketplace, and have found it a good place to sell at least lower price domains, but wish it was fully integrated, cross listed with other Marketplaces, and also that it was working for adding new domains right now!
I have not used Namesilo yet, but see from the vote it seems the overwhelming favourite so I should give it a look!
I only have a few with them, but was surprised Alpnames were not on the poll. They have good prices on many extensions, and seemed solid to use.