I haven’t used Radio Silence, but my impression from a glance over their website is that Radio Silence is rudimentary in comparison. It seems to allow only blocking of apps as a whole. I cannot see when that would be useful, as many apps use internet connections for legitimate purposes, e.g. to check for app updates.
Little Snitch is quite powerful. You can single out particular connections per application, such as by domain, hostname, IP address, port and protocol. You can assign them to profiles, which you can connect to particular networks. Little Snitch also has a real-time network monitor to show you what is going on. It can drive you crazy in the beginning though, as you will receive tons of permission requests that you have to deal with at least once.