Virtualbox or new pcs are most safe if u are trying to use fb/google. Multilogin is good but sometimes fb knows about it. Completely new environment is key here.
For newbie i would recommend multilogin because its easy to use and u dont need technical knowledge. But if u want free and relatively safe environment i would go for virtualbox with installed windows 7. Why windows 7? Because it has old Internet Explorer browser by default. And this version doesnt have support for WebRTC. You just pretend to be old grandpa and use old internet explorer

Than just duplicate a virtual machine and you are good to go with thousands of accounts. Cons: You will need plenty of disk space and of course good proxies(residential, 4g)