Air Galley to me might be even better than the Red Dragon. You can't stack them, but you can load them up with units and after the Air Galley moves, they all still have full movement. The extended range you can give to units makes them pretty powerful, game altering units. Also when it comes to ranged attack, you're comparing a short range breath attack to a long range javelin.
Against the ai the Air Galley can really abuse medium range archers and even dragons. By repeatedly attacking and withdrawing you can defeat armies you should have no chance against and often do it untouched.
Looking at the summoned units I revise my list as follows;
Gold Dragon - range attack flyers rule
Red Dragon - range attack flyers rule
Air Galley - range attack flyers rule, may be better than dragons due to transport ability. Load one with priests and ballistae. You can make slow units useful.
Black Dragon - ranged attack flyers rule, weaker than the red
Ice Drake - range attack flyers rule, weakest of the dragons
Air Elemental - flying and physical immunity also rules but they are vulnerable to priests and with weak melee they have to leave units with magic strike alone. They are also very hard to get.
Yaka Avatar - dominate on a durable unit, how many heroes can he get for you? You might never need to build units.
Incarnate - in the right situations, absolutely wicked, and you have a good chance of turning him into a syron elemental or even a hero. Let me loose with one in your backfield and you will dread these guys.
Nature Elemental - the true melee monster, a hero killer. You need to come at this one with one of the first three.
Astra - flying and healing, they get lots of xp pretty quick
Basilisk - doom gaze, swimming and respectable melee. I like them, but they need help to take walled cities.
Fire Elemental - ranged attack, tough melee, but a little slow.
Syron - tough melee but slow. Lacks important fire immunity.
Water Elemental - physical protection and swimming but little else.
Karagh - a cavern nightmare, unless he runs into archers. They hit hard but are surprisingly easy to hit.
Earth Elemental - slow, but at least it has wall crushing
Leprechaun - not very fearsome but useful. You just never know when a couple lucky shots will do them in.
Firstborn - fearsome, but they just move too slow. You will never win the race with these guys.
Reaper - more trouble than good, like the firstborn, you have better level 3 units you could build. If you are playing undead, I would rank them ahead of the firstborn because you can use them to destroy your enemy's economy.
[This message has been edited by Frogman (edited 12-03-2001 @ 06:25 PM).]