site-to-site all computers are connected via VPN by the router is doing the connection, no need to run the client connection.
remote-access-vpn each computer must create the vpn connection.
Which is better? Depends on how many at a location are connecting the other location. Cost of the router is usually much more as it must support site-to-site vpn. I have some servers that print to the other locations and I don’t want to screw with making sure the remote-access-vpn is up so I throw up a site-to-site.
Why not site-to-site? everybody sees each other and maybe you don’t want that and then you have to throw in an access-list to keep out the ones you want to lock out.
How to configure site-to-site vpn? Depends on the routers you have. Some are easy some are not.