From what I have picked up on different conversations is that if you do a lot of steady speed highway travel to keep it stock, if you pull additional loads get a slightly heavier one, if you P&G frequently it could help to get a lighter weight flywheel.
Personaly I'm leaving my flywheel alone as currently there is too much conjecture and not enough evidence as to what is better. I am kind of interested in this lightweight underdrive pulley though.
5 ribs - Ecotec Lightweight Crank Pulley - 2.0LNF/2.2/2.4: by Make and Model - Chevrolet - Cobalt - 5 ribs Ecotec Lightweight Crank - Car Performance Parts And Auto Accessories | MRZ Performance