It depends, if you have the ET Streets on it could be because of whats on the road or whatnot that would cause more or less spin... if its on street tires should spin hard in 1st and 2nd no matter what...
Powershifting is definately better mainly because when you think about it, it's like launching the car every shift, and the higher you launch the better.
I say keep working on it, and when you feel very confident, try it at the track at the shift RPM you use. I think that alone will put you close!