no difference more on amount of wires so say both decoders in one room then a qaud lnb will have 4 cables running all the way from the dish to your tv room, a twin will only have 2 until the multiswitch.
if decoders in diferent rooms then a quad will have 2 goes to tv room1 and other 2 to tv room 2, if twin the 2 wires to tv room 1 and then from tv room 1 to tvroom 2 another 2.
im not counting heart beat cable though so add 1 there
and some people have their multi switch out side as well right close by dish