Named pipes and sockets are not functionally equivalent; sockets provide more features (they are bidirectional, for a start).
We cannot tell you which will perform better, but I strongly suspect it doesn't matter.
Unix domain sockets will do pretty much what tcp sockets will, but only on the local machine and with (perhaps a bit) lower overhead.
If a Unix socket isn't fast enough and you're transferring a lot of data, consider using shared memory between your client and server (which is a LOT more complicated to set up).
Unix and NT both have "Named pipes" but they are totally different in feature set.