Pretty simple, if you want to mod it buy the series 1 with the vq25det in it. It is a much stronger motor and much easier to get power from it.
If you want the ultimate family car that is sexy and a great drive left stock get the series 2 with the vq35de in it.
Or if you are really rich get the series 2 and spend 20 grand on the motor then it would be the best option there is