@TB: interesting to see that experiences very. Many people in the rallye arena (like the 325 rally challenge) are changing from plate diff to Quaife, due to more traction (read: accelleration in difficult situations) over a plate diff.
I've had the pleasure of driving, on the same car (mine
), with both plate and Quaife diff experiencing the same thing: more grip with a Quaife diff then a plate diff. (read: faster times on track)
Driving with a plate diff an FWD is less comfortable then with a Torsen type diff.
Problem is: most (race) gearboxes have been set-up for plate diffs in the past; therefore many people still use them (and will (have to) keep using them)
Also less maintenance (like the gripper diff; driven that too) plate diffs are available, but lack the precision of a torsen type (eventhough some people prefer the more brutal way a plate diff works;
personal preferences apply here too 
).
From a technical stand point the Torsen diff is of a higher level then the (old(er)) plate diff types.
For most Alfa's (with FWD) there are no plate diffs available, but the choice between 2 Torsen type LSD'd: the Q2 from Torden and the ATB from Quaife, which is good news for the FWD Alfa people !
Anyway, let's discuss this over a beer at the Nurburgring during the international AO event