I have fond memories of victories with Articuno. Unlike that pathetic Moltres...
last night i typed out a top ten list but then my internet went out and i couldnt post it
Articuno is my favorite legendary bird too, not counting Lugia.
In competitive battling, Ice is a terrible type. All it's truly good for on the offense is destroying dragon/flying types. On the defensive spectrum, it only resist itself, and has a really bad weakness in Fighting. Having a weakness to Fighting was only tolerable in the first Generation when Psychic types were way too dominant for the rather weak and few in number Fighting types to want to show up in battle. Every generation, fighting types have gotten better though. Both in getting better moves, and better Pokes joining the roster of the type.
Articuno was sort of useful in Gen 1 competitive thanks to it's high special; every generation afterwards, special was split. It had high special defense, but it wasn't enough to sponge special attacks without a recovery move. It's Special Attack took a hit, and it no longer hit hard enough to match Moltres or Zapdos' power. The other two birds have always had better typing too. Electric/Flying is surprisingly decent defensively, although not amazingly so. Fire is a much better offensive type than Ice.
As generations went by, Rock types became more common, which hurt Zapdos', and especially Moltres' & Articuno's usability. Come Generation 4, the move Stealth Rock showed up on almost every team, be it a stalling team, an offensive team, or a balanced team.
Since Articuno's stats are geared towards being a defensive Pokemon, having very few resistances and such a huge (and more importantly, common) weakness made it unable to fulfill a defensive role reliably. If a Pokemon can't perform well reliably, then it ain't good. While Moltres isn't much better, at least it can still do massive damage thanks to Sunny Day boosting the power of Fire moves. Zapdos is no longer the best all-around Electric type anymore come Generation 5, but it's still a bit better than the other two.
... Yep, Articuno got the short end of the stick.
^ Huh... What made ya think that, I wonder?
Not that such would ever dissuade my liking of the frozen bird... It'l just dissuade me from using it in OU or Ubers.
And by any time, I mean any time right now.