RB30 without a doubt is a better base to start off with if you want a power house. Like i said before i wouldnt swap the RB26 for a 30 if my gt-r was going to be a mildly modified daily. Ive stroked my 26 to a 28 due to going big single otherwise i would had stayed with the 26 if i were going to keep the twins.
All the money you would need to spend on a 26/30 could be spent on other areas of the car likes brakes/wheels/suspension etc.