Math is the best one because of the transparency it gives for R&D and Exploration.
Tech is second because characters stats are a bit lacking in that.
Arts is third because it allows you to recruit one extra character, although it's still too close to the end of the build to really give an impact.
Leader is fourth because like arts it will get an extra character on the next build, plus it's the most helpful for solving argos riddles. however, once you know the solution, it becomes obsolete.
Humanities is fifth as it doesn't really give anything of worth right now.
Speedrunner is last since it actually handicaps you at some points.