One more hotly debated topic! I like Purolator - their "Pure One" has a built-in check valve which prevents help oil pressure loss at startup, particularly if the car has sat for a while. Part # PL14670. Whichever one you choose, make sure it has that valve!
Also, it's a good idea to "chase" the threads of the filter before installation, as the MGB filter adapter is pretty soft aluminum and very easily cross-threaded.