Ravencoin is dependent on others using it as a platform for it to have value (like ETH). I don’t know any projects building on Raven and don’t know the incentives for doing so. Saying it is a Bitcoin fork doesn’t mean much.
Grin is a currency - it’s not dependent on other projects.
Totally different imho.
Raven depends on people storing assets on the chain. The value is purely speculative at this point. There's hope that Ravencoin will be the Ethereum of STOs. Also, Patrick Byrne (overstock.com CEO) has been shilling Raven, overstock.com's Medici Ventures funds most of Raven's development, and there's speculation that the Tzero STO trading platform (mostly owned by overstock.com) will use the Ravencoin blockchain.
It's a shitcoin for now, but buying some would be a smart bet if you believe that the STO boom, that many are predicting, will come. Some speculate that as the last bull run was fueled by ICOs, the next will be fueled by STOs.
That's getting OT, so I'll try to tie that into this thread. As speculative assets go, RVN is a pioneering coin in a new space. Grin is stepping into an already-crowded space and doesn't offer much over XMR, IMO. With that said, some also predict that privacy coins will be a driver of the next big bull run. Even if Grin is playing 2nd or 3rd fiddle in the privacy space in a few years, it would still go parabolic in a privacy coin boom.
*I hold positions in RVN, GRIN, and XMR.