Ranking Dyna Birds - Moltres is King

For people who have limited coins, it may be important to decide ahead of time which bird you focus on buying extra particle packs for or going to meetups for if you can't do all three. The TL;DR is that Moltres, as far as I can tell, is likely to be the Best in Slot for Flying for a long, long time, and is probably worth getting a good one of if you can (not that IVs usually matter too much).

For Ice, Articuno is beaten by GMax Lapras, and for Electric, Zapdos by Gmax Toxtricity. If you're one of the unlucky many who are unlikely to ever get GMax pokemon, Zapdos will probably be Best in Slot for Electric for a long time (Xurkitree, Thundurus, Vikavolt, and Zekrom are the only Electrics that beat its Attack), so that might be worth getting a good one of, but Moltres picks up another win there as the Best in Slot non-GMax Fire attacker too!

As for Ice, Cryogonal has basically the same Attack as Articuno and both will be beaten by numerous Ice Types sooner or later (hell even Glaceon beats them, and we know for sure Eevee will be released as a GMax pokemon eventually so Glaceon will be included too, unless they do something bizarre like make it unable to evolve or its evolutions unable to Dynamax).

Meanwhile, the only Flying GMax is Corviknight, and Moltres has 251 to its 163 Attack, which is enough to overcome the GMax boost. In fact, of Flying type pokemon who also have a Flying fast attack, Moltres is 3rd only to Tornadus-I and Rayquaza, who it may be a long time before we see in Dynamax. (Edit: I've been reminded that technically Archeops also has a way higher attack. I kind of expect them to never release it in Dynamax because of how they intentionally gimped its attack pool so it's ineffective in raids to balance its absurd stats, but I could be wrong!)

There are maybe some other considerations for why you might want a good Articuno or Zapdos too, like if the Flying defensive type is ever relevant. Moltres will tank Grass very well, while Zapdos has no particular niche to explot. Articuno has the worst defensive typing, but the best defensive stats, which means the only pokemon it might be particularly well-suited to acting as a tank for are Ground types... until a Flying/Grass or Flying/Bug dynamax with decent stats is released, at least.

So realistically you're probably going to end up use other pokemon as tanks, which means again that Moltres is clearly number one. I'm hoping they keep cycling through these birds for a while because I'm going to be traveling during Moltres Dyna week and I definitely want a good IV one. I recommend others go hard on Moltres, if they have to choose between the three!