I have no idea what people end up choosing, but just thinking about it... I would say a 1-way or 1.5-way LSD. It may come down to how good the driver is.
The only critical time would be when your braking hard after the main strait into a corner. So as not to lock the front brakes, you go down the gears. But if you downshift too hard the rear tyres lock up. If both rears lock up, you may end up sideways. With an open diff, maybe only 1 rear would slip and you would still drive straight?
It's all about that split second, hard braking, downshifting, heal-toe, steering. Easy to get it wrong with or without a LSD.
My guess:
For an ugly handling car that is going to understeer, purposfully setup some oversteer just before the apex. So a locker or 2-way helps here. (WARNING: maybe viewed as "drift" by caretaker followed by a stern warning).
For a perfect car and driver:
A open diff will be fine. But an LSD could improve grip in places unless the track is also perfect.