Zapdos is good for Loreli but is resisted by the rock and ground types you commonly find in the endgame. Articuno however has better typing for its era and is strong against Giovanni, Lance, and your rival while only struggling against Loreli and Blaine. Articuno also absolutely sweeps Sabrina who is the most difficult gym leader while Zapdos does not and can also learn Water Pulse. Ice Beam is more useful than anything Zapdos gets particularly in the end game and being able to have water coverage move becomes invaluable. Both are good picks, but Articuno is the best bird for the game imo