If your a 100% alky burning drag racer - V2's for their peak power.
If you ride anything else - V4's for way better bottom end, peak numbers that are almost the same as 2's and throttle responce that's even stronger than 3's. The stock 4's outshine the 3's even if the 3's had the stuffer mod.
Some motors have shown as much as 7 extra HP of mid RPM power with the 4's.
So much, that if you swap your 3's for a new set of 4's you should install one size larger pilot jet.
This is all dyno tested info. Done on a wide variety of motors from bolt-on basic bikes on pump gas all the way thru alky burning draggers.