In The Lean Entrepreneur I discuss how to create a segment matrix: put your different segments in rows (hopefully these are NARROWLY defined!); in columns, come up with salient criteria to measure segment worthiness. It's ultimately up to you, but might include "Depth of Need", Budget, "Ease of Reach" (marketing), etc. Could even include things like "Matches Values." Be sure to write in such a way that a High-Medium-Low ranking is consistent across criteria. In other words a High Depth of Need is a good thing, so other high scores must be a "good" indicator. Rank each segment in the criteria High, Medium, or Low. It's OK to guess at this point, but your customer discovery should attempt to validate the values. It's likely that 1 or 2 segments will rise to the top.