Depends on the rest of your build and intended usage. This is in the race section, not general, so that's going to up the ante.
Here's my take on this from a low-buck, mainly street stance.
Go with a balanced kit if:
You are building a street car that will rarely if ever be at full throttle, the engine will be assembled at home with basic tools and you are not checking every tolerance and fitting each part. The engine will be more for bragging rights and wanting a bit more than stock.
Go with the unbalanced if:
You or a good, trusted machinist is going to double or triple-check and fit each and every component, the engine will be run hard and long and expected to produce consistant and reliable high HP, and you will use all the available power.

Most people fall in between the cruiser bragging that he has a 400+ small block and idling around town and the racer that has a combo that puts others to shame. I would lean toward expecting that some fitting and changes will be needed on the rotating assembly. Stuff like ring fitting, bearing or piston coating, cleanup of clearances, rod bolt changes or smoothing of the piston tops can all change the weights of the components. It makes sense to do all of this fitting and setup before final balance to me.

I would also add that if you are taking a bunch of parts to a machinist, it makes sense to have them responsible for all the special work done. If the cost is fairly close, have them do the balancing too.