Formally, 18 is still beta. And if JRiver develop their product as usual, it will be for another few months. I guess you will get two answers for your question. Psam gave you one of them, where returning to 17 was - for some reason - desirable. I swithced to 18 once it was available and have not looked back. Not one crash, and all the functionality I use is working perfectly.
Off topic: Honestly, maybe because I do not use it for TV, I have not noticed any change at all from 17 to 18 even if I know big things have happened under the hood. But if 18 develops similar as 16 and 17, I am almost jumping up and down in anticipation of what's to come. I will continue my support and buy future versions, no question about that!