Articuno

As the much-hyped first legendary bird species to be released in Pokemon GO, Articuno is a bit disappointing. Its base stats are defensively oriented in an offense-focused metagame, and while Ice type can be absolutely fantastic in many matchups, many other Ice Types have long since surpassed Articuno, making the expense of adding it to a raid team less and less appealing in the face of easier to obtain and stronger options.

Best PvE Offensive Moveset

• Frost Breath is marginally better than Ice Shard, though the two are very close. 

• Triple Axel is Articuno's best Charged Move option.

• Blizzard is on par with Ice Beam. Ice Beam has the advantage of being a 2-bar move, but its long animation time keeps it even with Blizzard. Regardless, both are inferior to Triple Axel.

• Icy Wind's low damage and long animation time (even longer than Blizzard) prevent it from being useful.
• Hurricane* offers no synergy with Ice-type moves outside of Grass Type raids, and is still sub-optimal.
• Ancient Power has no use on Articuno. 
• Return is basically worthless.

The greater energy generation from Ice Shard is much more valuable than Frost Breath's edge in damage output. 

Icy Wind is basically the main reason to run Articuno, providing solid damage and an aggravating attack debuff. Ancient Power is a solid option in the Ultra League, giving you a solid hit against other Articuno or Charizard. However, ever since AP got nerfed, Hurricane has seen a rise in play, giving a strong nuke against Fighting-types, and in general a hard hit many players may not expect!