I am also looking for other sites best used for trading NFTs, if you know any good marketplace too, let me know.
OpenSea is the most popular for the time being:
https://opensea.io/There are more that offer NFT trading like Enjin Marketplace and Rarible which you mentioned.
Also WAX:
https://wax.simplemarket.io/I've only traded on OpenSea and stopped after offloading some NFTs I was holding. I have no experience on the rest, but Rarible which you mentioned is legit.