I have both the FSM and an AllData subscription. I use the FSM maybe 5% of the time, and AllData the rest. (I also have the GM servicing disk that I haven't figured in here.) The reasons are that is is available anywhere I go, as long as I have a computer and internet access, it is much easier to navigate to find the information you need, has virtually the same information, and is a less "overwhelming" in particular for someone just starting out. You print out what you need, when you need it.
The minus is that it is a subscription service. The first one is the most expensive. Adding vehicles then get a discount, and renewals are also discounted.
Black 2000 SSEi, Silverstar Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, drilled 180 degree thermostat, Intense FWI, PCM, shift kit, and 3.4 Pulley. Solid front mount.