Remix OS and Phoenix OS are just two Android distributions - both based on Android x86. So in terms of hardware support, they might be similar. Phoenix OS seems more refined and ready for market, Remix OS is still just beta and has a lot of bugs. On the other hand Remix OS has a much bigger community, help pages, forums and users - with Phoenix OS you are on your own.
All that said, there is a third option. You could simply plug your Android tablet to a keyboard/mouse/screen and forget about all the Android x86 fever. Your hardware will be fully supported, have access to an official Google Android build with all the support included and in the long term there will be less hassle. And now with Android N on the way which supports Remix OS like windows, you will never notice any difference. I myself am going this route. I will wait for Android N tablets, buy a sufficiently performing one and plug it to some peripherals - instant Android desktop, fully supported by Google. No tricks, no hacks, no unsupported hardware.