To be honest I think there's only a handfull of different situations in which there's much of a difference. And in most situations you have quite a lot of options none of which are really bad. - Need bodies to hold an objective or stand in the way? -> skinks - Need bodies that actually put up a fight? -> Knights, guard, maybe warriors if they only need to put up a "small" fight. Potentially rippers/terradons if you expect their superior damage to make up for their smaller numbers, kroxigor could also work on account of them having an anti-horde weapon and thus potentially being able to destroy the competition for an objective easily. But basicly any Multi-model unit bar skinks can work for this (unless we get 40 man summons at some point...) - Need to destroy stuff? -> Rippers, terradons, pretty much any big dinosaur, potentially kroxigor against hordes. - Ranged firepower? -> bastiladon with solar engine, razors or salamanders. - Need to replace a fallen hero, monster or wiped out unit? -> basicly anything. - Need to hold the line and push back a souped up doomstar or some such? -> Bastiladon, guards if they aren't going to immeadiatly be blasted away by mortal wounds, potentially other stuff if you can ensure you get to attack first. - Surprise rear charge? -> Stegadon, Troglodon, potentially any saurus unit if you have something in place to boost its charge. There's also quite a lot of overlap between the various situations and except from just needing more bodies to stand in a way all of em have a fairly large pool to choose from. To be honest, I think the most likely conclusion of the thread is either going to be "bury your opponent in skinks, he can't kill them all and maybe occasionally summon something else if you're in need of it" or "just summon what you want, it doesn't matter That much that it's suboptimal it'l probably work anyways, except for warriors, those are terrible to summon...".
It has only happened in two games for me (out of dozens upon dozens), but a summoned unit of 20 Club Saurus Warriors is pretty solid for retaking an objective that has been swarmed by 20'ish enemy models. Both matches that I used them I had cogs on the field and set it to movement knowing that I was going to summon them. I also LoSaT my Saurus Astrolith Bearer to the area I planned to summon the warriors, so I ended up with Proud Defiance. Both instance were the winning play of the game though. Without cogs or the Steed Constellation Saurus Warriors are not worth the Celestial Conjuration Points. However, in the right circumstance they are very good at objective recapture. Skinks normally won't help thin the enemy holding units down enough and the other options have too few bodies. Warriors are definitely niche summon choices though.
Meh it's that at 18 summon points there's no Knights or guards equivalent otherwise those would probably have gotten the job done as well. I'd also not be surprised if the kroxigor would be able to pull it off as well with their anti horde waepon (depends a bit on the situation). Depedning on what's holding the objective and how much time you have left even the big dinosaurs could potentially get a job done (tad risky though is it'd involve killing everything..) Kind of lame though, the one situation where warriors shine as a summon is the one where they are the only relevant option to begin with. Skinks won't move anyone of an objective, and with "only" 18 points to summon this is the only way to get more than 5 usefull models on the field. On that note, I feel like there's several bits "missing" in our summoning table. Why are the warriors the only ones we can summon at two different sizes? Where's that option for well, everything else basicly. Also, the insistance on making all summons multiples of 6 is a tad weird.. especially considering the astrolith generates D3 points. There's a potential to waste 5 points there no matter how much you summon. And it also means that you get a weirdly tiered system. Some of those 12 point summons should really be 10 or 11 or 13, but now they're all the same value. It's a bit odd. But that goes for all the summoning tables for all factions I think, they all use this tiering system which isn't necesarly the most balanced approach to it.
If that's what you get from this thread good for you, personnally I like hearing about in-game experiences from a large pool of players, not just my own theoretical takeaways.