With the data you've provided, it's hard to make any recommendations.
In particular, you don't say anything about the applications that you want to run. What you want to do with your board will dictate how many cores you need, how fast they need to be, which interfaces and peripherals you need, etc.
There are a few types of research that you can do to help narrow down your search:
- determine what sort of sensors and devices you need to plug in, and make sure the board you pick supports them
- search the internet for other people doing similar projects, and look at which computers they're using
- look at the ROS installation instructions and search the internet for guides on installing ROS on each board that you're considering. skim through each guide to get a sense of how well polished it is and how complex it is. Poorly-polished or complex guides indicate that it will take more work to get ROS running on that particular board.