Tier list

A tier list is a ranking of each character's metagame, based on tournament settings. It indicates how professional smashers expect each character to be able to perform under tournament conditions. Tiers thus measure the potential of each character based on all currently known techniques and strategies that have been shown to be useful in tournaments. Tier lists are common in fighting games as well as many other competitive games involving a large selection of characters, such as Pokémon.

Individual match-ups affect but do not entirely determine a character's ranking. Sometimes a character carries an advantage over a higher-ranked character — such a match-up is known as a counter. For example, if Pichu held a winning match-up against Fox but suffered from worst matchups than Fox against every other character in the game, Pichu would be considered to counter Fox but still be ranked lower than him on the tier list. If two players at the height of the known metagame fought Fox vs. Pichu, the tier list alone could not predict the average outcome of the match.

SSB tier list
This list is cited from a GameFAQs post and generally reflects the sentiments of top-level Super Smash Bros. players.

SSBM tier list
This is the ninth and last Smash Back Room Super Smash Bros. Melee NTSC tier list. It is current as of 14 October 2008. Note that while some characters appear to have equal scores, the scores are rounded with the only true tie being Captain Falcon and Jigglypuff.

SSBB tier list
This is the second version of the tier list for Brawl. It is current as of 5 January 2009. The next tier list will be released on June 5th, 2009. 

Additionally, the Smash Back Room released a graph that shows the intervalic rankings of the characters in relation to each other (each character was scored on a 15 point scale):

Controversy of the Existence of Tiers
For a comprehensive detailing of the arguments in favor of the existence of tiers, see this page.

Controversy arises periodically over the existence of tiers, most notably during the "tier wars" at GameFAQs and Smashboards. Some smashers, called "anti-tiers," argue that every character can be played equally well. In support of this argument, they claim the tier list creates a cycle in which players choose only higher-tiered characters, and thus only those characters develop an advanced metagame, thereby reinforcing the tier list.

The unanimous consensus of competitive players is that tiers do exist. They argue that it would be almost impossible to balance a game of unlike characters; without specific redesign, characters would have the tendency to fall into tiers by dint of their myriad variables (differing attack power, running speed, etc.). Furthermore, the developers cannot foresee top-level strategies, and thus even their deliberate efforts could fail to balance the game at a professional level. Years of empirical results support this conclusion as well; national tournament-winners of Melee almost always use Marth, Fox, Falco and Sheik, though anti-tiers typically attribute this success to the preferences of a few skilled players rather than the abilities of the characters themselves.

The list itself is subject to change. Optimal strategies for each character shift over time, changing the metagame and the tier list. Anti-tiers use this point to argue that the tier list cannot be true if it changes. Pro-tiers respond by pointing out that it may be true for a particular, static metagame, and that this argument doesn't weigh against the existence of tiers themselves, but merely against a particular metagame.

Tiers exist at all levels of play, though the rankings are highly changed from casual play to competitive play, due to different strategies and a different metagame from the tournament level.