1. Toronto FC
The skinny: Last year, TFC hosted the MLS Cup, only to lose on penalty kicks to the Seattle Sounders. This season, Toronto FC steamrolled to one of the greatest regular seasons in league history. Toronto FC set a record for most points in a season with 69, beating the previous mark of 68 by the Los Angeles Galaxy in 1998. TFC's plus-37 goal differential is the best since that 1998 Galaxy team had a plus-41 goal differential (it should be noted that the 1998 Galaxy played a 32-game schedule; MLS currently plays a 34-game slate). That 1998 Galaxy team, however, didn't even advance to the MLS Cup. TFC would like to avoid being a footnote in MLS history.
After having already won the Canadian Championship and Supporters' Shield, Toronto FC will be in the conversation as the league's greatest-ever team if it can also win the MLS Cup.
The player to watch: Sebastian Giovinco. After being lost in the wilderness for its first eight years of existence, Toronto FC immediately became a playoff team once Giovinco joined the team in 2015. With Giovinco and Jozy Altidore, TFC has a potent one-two goal-scoring punch that is very difficult to stop.
Major League Soccer playoffs: Schedule, game times, TV info
Milestones: Toronto FC sets MLS record, Atlanta breaks attendance marks
Best goal celebration: Jozy Altidore tries to head beer thrown at him
2. Portland Timbers
The skinny: The Timbers followed up their MLS Cup triumph by failing to make the playoffs in 2016. Portland is back in the postseason after finishing with the best record in the Western Conference, and figure to be in a hotly contested playoff field out West highlighted by the three Cascadia teams. The Portland Thorns won the NWSL championship, so could the Timbers join them as champions for a rare women's-men's same-city double?
The player to watch: Diego Valeri. Valeri had a record-setting 2017 season that could earn him the league's MVP award. He scored a goal in an MLS-record nine consecutive games. Valeri is also just the second MLS player ever with at least 20 goals and 10 assists in a single season.
3. Seattle Sounders FC
The skinny: The defending MLS Cup champions have a strong shot at a title repeat. As their conference's No. 2 seed, the Sounders will get at least one game at home, where they are nearly unbeatable in front of their famously raucous home crowds. What also potentially lies ahead is a tantalizing Western Conference final showdown between the Sounders and Timbers, whose rivalry is one of the best in all of sports.
The player to watch: Clint Dempsey. Dempsey picked up a red card in the regular-season finale, and will miss the Sounders' playoff opener. As the Western Conference's second seed, the Sounders will get "Deuce" back for the usually very critical second leg of a home-and-home playoff series. Dempsey missed last year's MLS Cup title run after an irregular heartbeat sidelined the U.S. men's national team stalwart for a significant amount of time, and will be highly motivated once he finally gets back on the field.
4. Atlanta United FC
The skinny: As Toronto FC chases history, Atlanta United would like to make some of its own. Only one expansion team in league history has ever won the MLS Cup, and that happened in 1998 when the Chicago Fire won when the league had 12 teams. MLS currently has 22 teams, and Atlanta is the first expansion team to reach the playoffs since the Seattle Sounders in 2009. Like TFC, Atlanta sports one of the best goal differentials in league history (plus-30, good for fourth all time). Games at Mercedes-Benz Stadium — where Atlanta has twice set single-game attendance records — should be an incredibly difficult environment for opponents to prevail.
The player to watch: Josef Martinez. Martinez missed a huge chunk of the season due to a foot injury suffered in a World Cup qualifier for his native Venezuela. However, he managed to score goals at an alarming rate: 19 in 20 games. That run included back-to-back hat tricks in September.