[The Panther]

As for saving gems for higher level summoning spells, I try to do this as much as I can.

Earth - Mechanical men are vastly superior to clockwork horrors as well as pretty much any other earth summons. You can't always wait for this, as your neighbors often times interrupt grand plans!

Death - The death summons are so very powerful at the higher levels, that I also like to hoard those for a rainy day. Unless you consider Bane Lords to be a lower level summons, as I tend to use that one a lot. Black Servents are very good for fever fetishes, clams, and exploring.

Water - Not very useful for summons. I suppose getting the sea troll kings is done just for the one water gem income per turn and the attached water skill to build clams. That hardly counts, though, for the goal is usally clams and not troops here. The sea trolls themselves are useful fodder, of course, but the fact that you have to pay them upkeep renders them practically useless.

Nature - pretty much everybody I know uses the ivy crown for monthly ritual vine ogres, one of the best bargain summoned troop in the game. Later, the fairy queens are good for the healing ability.

Air - I usually save up the 45 gems for draconians. The leaders can summon more, which is very nice. And they fly, which is a HUGE bonus. The hawks have the gigantic disadvantage that you have to pay them upkeep.

Fire - I don't summon fire much, for the gems are typically better used to convert to money for buying more mages.

Blood - Devils, devils, and more devils. Is there a better low-level summoned troop for the gem cost than a devil? I don't really know of one. Oh, and the ice devils and arch devils too. They are still devils, though. Don't foget soul contracts also, if your neighbors leave you alone.

Astral - Are there any astral summons worth casting other than those high-level abominations that require 25 gems? I don't really know of any.