Definitely less wheel-spin is quicker. Sometimes a little slip puts some temperature into your tires and you get better grip, depending on the characteristics, but generally minimizing the wheel-spin is the way to go. However, if the clock starts as the lights go out, dump the clutch – even if you get some wheel-spin is perhaps not a bad idea. If you try to engage the clutch cleverly and conservatively to control wheel-spin, this can make a delayed reaction and in the end it could result in a slow start… Anyway, even if you dump the clutch, try to find a way to minimize the wheel-spin.
In F1, there are some tricks. They have a double-paddle clutch system where you can release one side as soon as the lights go out, so there’s no delay for reaction, but the other clutch paddle is waiting at the optimal half-engaged position. Also there are special engine and throttle maps for the start, so that’s what makes it possible to make a nearly perfect start with almost no wheel-spin.
Next, timing for the upshift – unless the engine power starts surging too much at very top end, you should upshift at the maximum revs. After the upshift, next gear should drop near the maximum engine torque, which is ideal. Do you have a non-synchronized gearbox? If so then you won't need the clutch for the upshift. Just a very quick lift of throttle should allow you to upshift… Good luck!