Jim Thompson writes:
I presume I should use the "A" terminals, though I have not a clue,
I've never done anything but plug CAT-5 cables together before ;-)

Which is correct?

They're two different standards, both "correct". I use the B
configuration, which AFAIK is more reliable for higher speed ethernet.
Check your existing cables and see which they use.

http://en.wikipedia.org/wiki/TIA/EIA-568-B
http://en.wikipedia.org/wiki/Category_6_cable

I had one long cable that didn't work with the A wiring (packet loss),
but did work with the B wiring. YMMV.