Radio Silence and Little Snitch are both great apps, and this is a totally biased comparison. Take it with as many grains of salt as you need.
This comparison assumes that you want to block apps from accessing the net.
Radio Silence is an American trio of filmmakers based in Los Angeles. The group is known for Ready or Not, V/H/S, Devil's Due, and Southbound, as well as their previous work together as Chad, Matt & Rob. I just took my tech license the other day and passed it KJ7QVY. Azduststorm; Sep 18, 2020; Replies 18 Views 880. New Tech licensee.
It really depends on what you want.
The two firewalls have two very different goals.
Little Snitch gives you a great amount of control. When a new connection is made, Little Snitch asks you if you want to allow it. A new app wants to access the network? You get a pop-up. An old app wants to connect to a new server? A new pop-up. Little Snitch will remember the choices you make, but ask you about any new kind of connections.
Radio Silence takes the reverse approach. If you want to block an app, you add it to Radio Silence's list. After that, the firewall is totally invisible. Blocked apps will get blocked, and the rest will go through. There will never be any pop-ups or interruptions.
It really boils down to this. With Little Snitch, your work is interrupted with a pop-up window every time something new happens. Some people enjoy that level of micromanagement. Some don't.
If you want to adjust your firewall through real-time pop-ups, go with Little Snitch ($30).
If you just want to block a few apps, Radio Silence ($9) is probably the better choice.
Both are excellent apps in their own game. You can find much less biased overviews on other sites!