Psion
Adventurer
TerraDave said:What makes the other two so great, and what is in the AGM--I know nothing of it. (actually it would be great to have a comparison of AGM and DMGII)
If in doubt, turn to the reviews page, padawan. (There were also some pretty decent threads discussing the book if you have search available.)
Here's my review on the reivews page.
Between the AGMG and DMGII, I think I prefer the AGMG. If you are a modest to intermediate GM, the DMGII probably has more for you to "take it to the next level". The AGMG has a bit of the same style of advice, but if you have already read Robin's Laws of Good Gamemastering (which overlaps a bit with the first chapter of DMGII), you might find the perspective of AGMG's advice fresher. The AGMG is a bit more about experimenting and expanding on your gaming experience and has more pure utility material and variants that will be of more use to more advanced GMs.