Normally, the feed arrangement for Ku band on a prime focus dish has a C120 flange fitting so a C120 LNB is required. Popular makes of C120 LNB for Ku band are Inverto and Invacom. Personally, I have a preference for the Invacom C120 LNB's as they have given slightly higher signal levels compared to Inverto in tests I have done.
The price of quad output C120 LNB's has gone up a lot recently. Unless you need 4 outputs, a good LNB for a prime focus dish would be an Invacom dual output C120 LNB or an Invacom single output C120 LNB.