Lineup selection is one of the largest influences a coach has on a specific match. In an ideal world this would mean putting the names of his best player at every position of his standard shape on the pitch and having them play. In that ideal world Alonso is not injured, Yedlin is not with the U20s in Turkey, Joseph is in good form and the Johnson/Martins pairing has practiced together.
Clearly the world is not ideal. When Sigi Schmid selects a lineup for this weekend's game all of those factors and more will be taken into account. His Ideal XI can be inferred, just as Plato recognized that an ideal triangle must exist. The Ideal XI would be powerful and performing at the strength and power that now only exists in numbers, rankings and estimates.
Sigi will instead deal with how to get Lamar Neagle onto the pitch to start. It is a choice between shape of the team and role of the player. Neagle offers a third scorer in the attack like few teams in the modern era of MLS had. Since the elimination of the shoot-out and golden goal eras to break ties MLS has only one team (San Jose last year) with three double-digit scorers and one that missed that mark with three at nine goals (KC 2011). In fact only nine teams have seasons with two double digit scorers since Seattle Sounders FC joined the league. Getting the most out of his three options is one of Sigi's larger challenges this year.
Servando Carrasco will also compete for time. His performances so far are generally strong with his more developed passing game he is not just a stopper now. Carrasco broke out of a sophomore slump in a big way. Since Alonso is coming back from an injury there may be caution with his playing time (we'll learn more this week) and Joseph's up-and-down performances are a cause to question his status in an ideal XI.
The questions about the starting lineup will continue to be addressed on a match-by-match basis. While there is an ideal that sits in the heads of the Coach and GM, it may never be seen. The influence it exerts on potential additions to the roster during the upcoming transfer window will be evident, but a fully healthy squad is rare.
Theory of the Best XI is fine. In practice there is a group of about 15 men, maybe more, who could start a given match. All guesses are valid, but only XI will start and there are more that deserve time. It may not be the Best XI in theory, but it will be another XI that has an oft-injured and lineup reduced squad in Playoff position.