Unix sockets are a little bit faster as you don’t have the tcp-overhead. If you realize this performance loss is a question of server load. If you don’t have very high server load you won’t recognize it.
If you use Jails (FreeBSD) or some other virtualisation technology to separate the e.g. MySQL-Server from the Webserver, you often use the tcp/ip setup instead of sockets. The firewall rules need to restrict the access though.
You need to find out if your system is under heavy load so that a socket is a must or you can focus on a nice system design (separating services), then a tcp/ip solution would be better.
So make a long answer short:
Yes, there is a performance difference, sockets are faster. If you are not suffering high server load, just choose what fits better to your system’s design.