There is never an obvious choice!
Let me explain why: in Chaos, it can sometimes be beneficial to build Hydras instead of Cyclops on small maps... and in Nature, you might get stuck on Elves, so it's better to go for Tigers, and then Griffons, but they are more expensive... and Unicorns can blind. So, is it a Magic Dragon or a Phoenix? Different maps require different priorities! If you have a better archer, go for the Magic Dragon! If you have a Druid, go for the Phoenix...
The only almost undisputed choice is Djinns; they are both archers and mages!