I've used the King.
I think it was ~80% IFR ops, which really, is most of the mystique of the G1000 -- everyone can figure out how to direct-to
It was typical King (campy, practical, Martha's hair helmet), but it was overkill for me, even as an IFR pilot. I ended up skipping around the last half of the material. I bought it when it first came out too, at $299.
I have no experience with Sporty's, but I did think their IFR training DVDs were appalling and I haven't tried their stuff since.
I liked Trescott's book on the G1000.
I haven't looked into anything more recently than these.
The Garmin Pilot Guide and a ground power unit are really worth trying out if you have access to the plane. I think that Garmin book is pretty comprehensive if you can spend the time finding what you need, or just going trough it all on the ground.
$0.02
- Mike