Connection/invite problem/ server choice?

[--Fame--]

Hello lately i haven't been able to invite my friend to squad it keeps saying could not deliver or even i couldn't see him in my friend list online and he is actually online cause i am talking with him teamspeak and i made sure that the firewall is not blocking anything and of the proxy setting but then i though maybe it's the server so how do you know which server you have the best ping or connection too and does anyone faced the same problem i had and fixed it? i would appreciate the help

Thanks :D