The question at hand from an MLS noob...
"I need to get into MLS to understand who all the teams are and the relative hierarchy..."Well, MLS fan-to-be, here's one man's attempt at putting it in perspective for you, in alphabetical order...
Chicago Fire = Colorado Avalanche (NHL)
They showed up on the scene and won, quickly. The 'Lanche's title in their first season nicely mirrors the Fire's 1998 inaugural season championship. Chicago has frequently challenged for the MLS Cup, and has a bitter rival in FC Dallas just as the NHL's Denver club has intense games with the Detroit Red Wings.
Chivas USA = Memphis Grizzlies (NBA)
Here's a relatively new club (discounting Memphis' tenure in Vancouver) that is in its second season, is making all the right moves, and appears headed for a playoff berth. I doubt the Grizzlies draw a huge Mexican crowd in NBA cities as Chivas does, but I believe that "The Chivas Way" will deliver a championship to the LA-based club in the next three years.
Colorado Rapids = Toronto Blue Jays (MLB)
Um, they're ok, but just as Toronto has finished in the middle of the AL East for the last five seasons or so, the Rapids have a similar track record of playing bland seasons which aren't awful, but aren't good enough to contend for a title. A true vanilla team with little personality.
Columbus Crew = Tampa Bay Devil Rays (MLB)
Ecch. Here's a team in a small market that has a stupid name, draws few fans, has little history of success, no stars, and a small payroll. The Crew does have the first soccer-specific stadium in the US, which gets it exactly one brownie point. When the US plays Mexico in Columbus Crew stadium, it's a big deal. As of late, however, there's nothing to be excited about this Crew.
DC United = Pittsburgh Steelers (NFL)
A recent return to championship form for MLS' most successful franchise. A franchise player in Freddy Adu a la Pittsburgh's Big Ben (though Freddy doesn't ride motorcycles). Both clubs are lethal when in form, have iconic coaches, and strong fan followings. Both are usually the teams to beat. DC is currently seeking "one for the thumb."
FC Dallas = Anaheim Ducks (NHL)
Both have silly names. Both are quality teams. Both have distinctive uniforms. Neither have won a championship. Both have relatively new arenas outside of more populous cities. FCD will be trying to reach the league final in its own house for the second straight year. They could just do it.
Houston Dynamo = Tennessee Titans (NFL)
Forgetting the NFL club's poor start to the season, the Dynamo is a good club with a history of success that left town for greener pastures. The Steve McNair/Eddie George era Titans are a nice mirror to the Dynamo's Dwayne DeRosario and Brian Ching. Houston/San Jose has two league titles to the Tennessee/Houston's none.
Kansas City Wizards = the 1985 Chicago Bears (NFL)
The 2000 Wizards and the Super Bowl Shuffle Bears each won their lone titles with stifling defenses. Though Da Bears have been on an upswing of late in their re-made Soldier Field, the Wizards, currently hoping for a new home of their own, have taken a downturn of late. KC is in danger of missing the MLS playoffs for the second straight year... which is hard to do in MLS.
Los Angeles Galaxy = San Francisco Giants (MLB)
Both clubs have a superstar that people even love or hate. Sure, Landon Donovan hasn't been accused of taking steroids a la Barry Bonds, but Donovan's lack of desire to push himself in a top European league stunts the US National Team star's development as a player, hurting the US' chances in future World Cups. This in turn pisses a lot of people off. The Galaxy have won two recent league titles, something SF can't boast.
New York Red Bulls = Arizona Cardinals (NFL)
Yecch. Both of these teams have histories of being miserable both on and off the field. The former MetroStars have had 10 head coaches in 11 seasons. They've never advanced to the league title match. However, as with the Cardinals, a new infusion of cash and a new home (for NY, to open in 2008) portend better days ahead.
New England Revolution = Indianapolis Colts (NFL)
The Revs have recently improved against their history of bad form to become one of MLS' top clubs. New England has reached two MLS Cup Finals in the past five seasons, but have been unable to win the big one. While the Revs don't have a transcendent player a la Peyton Manning, the club does have a cadre of stars (Clint Dempsey, Taylor Twellman, Pat Noonan) that can score at any time.
Real Salt Lake = Houston Texans (NFL)
RSL is a new club in its second season. They haven't had success on the field with a roster full of aging stars, but they have attracted large crowds. As with the NFL, however, clubs can radically re-tool from season to season and may be a force in years to come.