Regular GM Harmonic Balancer or underdrive?
 

I'm changing the wobbly crankshaft harmonic balancer and pulley and was contemplating putting on an underdrive pulley. Is there a benefit?

An under drive pulley will cause your accessories to spin slower. No advantage for a street driven car. The consensus on the forum is to avoid the stock GM pulley and go aftermarket, ATI, Powerbond, etc.