Here's a thread for general tactical discussion within MLS, inspired by needing a relevant place to link this decent, if a little cursory, article examining the drift away from a 4-4-2 in recent years.
http://www.unusualefforts.com/mls-formations-and-tactics/
A sample:
"At the end of the 2015 MLS season, 11 of the 20 teams were using a 4-2-3-1, though its effectiveness depended on the skill level of the players. In both the 2014 and 2015 MLS Cups, the winning team fell back on a 4-4-2 (LA Galaxy and the Portland Timbers, respectively), but as the 2016 season begins to take shape, many teams are exploring other options. Of the top 12 teams at the end of April, four were consistently running a 4-4-2. Two of the eight others have used a 4-4-2 at least once this season, but most are using a 4-2-3-1 or a 4-3-3."
http://www.unusualefforts.com/mls-formations-and-tactics/
A sample:
"At the end of the 2015 MLS season, 11 of the 20 teams were using a 4-2-3-1, though its effectiveness depended on the skill level of the players. In both the 2014 and 2015 MLS Cups, the winning team fell back on a 4-4-2 (LA Galaxy and the Portland Timbers, respectively), but as the 2016 season begins to take shape, many teams are exploring other options. Of the top 12 teams at the end of April, four were consistently running a 4-4-2. Two of the eight others have used a 4-4-2 at least once this season, but most are using a 4-2-3-1 or a 4-3-3."