R31 for sure. Just look at the inside of a ser 3 skyline compared to a VL.
RB30E's vary, mine is crap up top, some have good top end, some are more powerful for no apparent reason (bloody kryz). Which is faster will vary car to car.
In my experience, the 31's drive better than the VL's overall.
Wheel selection is a pain, but R33 aftermarket non turbo, and silvia wheels fit, so this makes it a bit easier.
Mine has been really reliable. The diff is fine. I did two or 3 skidpan days before I even changed the oil in it. It looked like someone had crapped in the diff when i dropped the oil. Did another 3 skidpan days and its fine. Used a diff treatment and full synth fluid and its quieter now. In 4yrs Ive had the following breakdowns: Clutch slave and master cyl, Dizzy (probably the bloody CAS), water pump, water pump gasket, and power steering pump, and its had a seriously hard time.
The only reason I would buy a VL over a 31 is if I had a blind loyalty to holden.