Personally I think good summoning candidates are whatever you can field, where it will be effective, while keeping your Slann safe if you have to teleport him. Frog boy can easily drop a Pallisade in front of himself with a spare spell slot if you're only summoning cheap things, which helps.
Personally I like the idea of dropping in Razordons; they're pretty cheap, have an effective 12" shooting attack on a one-model basis, and can be used to punish enemy charges against them or nearby units, all of which happily work around the 9" minimum summon distance and inability to move that turn. And they're only six points, so with a Vortex, Cogs, Kroak or an average Astrolith roll you can bring in two per turn! I can see the value in saving up for a bastiladon given that they stick around for a long time, but most other things that level I would avoid - Carnosaurs are too fragile if focussed, and not being able to move while being a melee-only unit would leave them in a bad place post-summon. If you need a tanky units your opponents will focus, the Bastiladon will do that much better; if you need to support existing troops, bring in a hero who buffs those troops; if you need a disposable screen, Skinks>Saurus because they're cheaper and get to shoot.
Part of the point of the EotG is that it's other effects are still useful. Before the changes to summoning, you were fishing for 18s and the mortal wounds just made it a cheaper Bastiladon for one round. The summoning uses of EotG are a bit different, since it happens in the hero phase, not at the end of the shooting, so whatever unit is summoned gets to move immediately. Again, 20-man units of Skinks are a good choice if you need a disposable screen, whereas if your EotG/Slann/Astrolith bunker is pretty safe, but the Terradons and Ripperdactyls aren't a bad choice either due to their speed and devastating attacks. Their glass cannon nature is offset a lot if you can just summon them again the moment their models are off the board, and terradons can get scary in repeat waves since fresh summons get their drop-rocks back.