Also what drove the nobility and yeomen to joining one Order over the Other? Templar vs Hospitaller vs Teuton vs Swordbrother vs all the other smaller ones?
As William Urban said in "The Teutonic Knights", greed and a desire for secular power and authority influenced men to join German knightly orders. The Teutonic Knights were the biggest German order, but that also would have meant that it would have been harder to make money or grab lands and territory quickly as a Teutonic Knight as opposed to a Swordbrother or a member of one of the smaller orders. It was not exactly the same sort of situation as the Wild West in the United States, but not completely dissimilar, either - very high risk, but the possibility of very high reward if you happened to get in on the ground floor of a small, fringe Order that struck it rich.
This was not entirely unlikely. Duke Conrad of Masovia, a Polish lord, made a particularly bad decision as far as his interests were concerned - he allowed the Teutonic Knights to keep what they conquered, so long as they kept Baltic pagans away from his lands in Poland. According to both Urban and the Chronicle of Henry of Livonia (among other sources), the patrons and/or sponsors of the knightly orders occasionally made concessions or policy decisions that offered knightly orders huge opportunities to establish quasi-nations of their own. Eastern Prussia (which survived from the 13th century to the end of World War I) originally derived from the Teutonic Knights' conquest of Baltic territories. With that kind of thing going on, it wasn't absolutely crazy that someone could have worked out how to strike it rich going to war against the Baltic pagans.
Urban also points out that many of the knights did not come from established rich families - a second son of a poor ministeriale* family would not have inherited anything, but there might not have been much for his older brother to inherit in the first place. Further, knights received absolution for their sins and the Teutonic Order (though possibly not the smaller orders) would sometimes help knights who had money or bankruptcy issues. Joining a military organization to get financial help is, was, and always will be common.
Part of the reason for the establishment of the Teutonic Knights in the first place was ethnic/national/however you want to look at it issues from the Templars and Hospitallers. Predominantly French and Italian, they tended to focus on their own countrymen in the Holy Land - French and Italian pilgrims, etc, got preferential treatment. Insofar as there were "German" pilgrims at the time (instead of a hodgepodge of Saxons, Thuringians, Bavarians, etc, etc, etc), eventually they got tired of being second-class pilgrims. If you wanted to join up with other Germans and fight the Muslims (or the Cumans in Eastern Europe or the pagans in the Baltic region), you would have to join the Teutonic Knights or one of the other German orders.
In terms of other motivations, there are always the old standbys - a brother or a friend joined a specific order and you wanted to go with them. An uncle or a cousin was killed by the Semgallians or Samogitians and you wanted to get revenge. Some recruits no doubt wanted to spread the word of God, and decided (probably for linguistic or ethnic reasons) that the Teutonic Knights or one of the other German orders was the best way to do that.