Bird counters

First it should be noted that there's no guarantee the birds will return to T5 raids (at least anytime soon). The odds of this happening will decrease further should they be confirmed as quest rewards.

For Articuno, Entei is probably the best of the recently-released lot, with Raikou a close second. Others you could look at are Lunatone, Solrock, Blaziken, and Metagross.

For Moltres, Kyogre has to be up there, while Rayquaza with Ancient Power would also pack a punch. Raikou is a solid option here. Lunatone and Solrock, again, would be decent.

Finally, for Zapdos, Raikou would actually make a solid counter, resisting electric-type moves but dealing regular damage (since Zapdos doesn't resist electric-type offense). Other than Raikou (and a generalist like Rayquaza), however, I feel you'd be best off with the same old faces for this one.

Shoutout to Mew for being a decent counter for any and all of the three given the appropriate moveset.

Zapdos counters indeed haven't changed much, just use Golems.

Articuno: Golem has best DPS but is glass. Entei is by far the best overall counter, tied with Raikou for DPS but much tankier. Solrock and Lunatone are actually up there as glassy DPS attackers, followed by Moltres, Flareon and Blaziken, which edge out IT/SE Tyranitar by a bit of DPS. Metagross and Ho-Oh are solid tank counters but neither has as much TDO as Entei.

Moltres: Golem is still king, although Kyogre is close behind and packs more TDO. Solrock, Lunatone, AP Rayquaza, Raikou, Zapdos and Gary are all good options to fill in leftover spots.

Is it just me or does it feel most people underestimate or forget how great golem is?