If you found yourself aligned with most of the qualities of “lighter” strings outlined here, choosing a string labeled “Light” is a good starting point. If you’re finding finger-fatigue is an issue, or you wish it was easier to bend notes, try extra light or custom light gauge strings.
If most of the qualities prescribed to heavier strings appealed to you, start with strings that are labeled “Medium.” While Martin does not recommend using heavy gauge strings on Martin guitars, we want to paint a complete picture of string gauge options. Some guitarists use heavy gauge strings for amplification, sustain, drop/down tuning, or tuning stability reasons.
One thing to keep in mind when trying out a new string gauge is to make sure your guitar is set up correctly for the gauge you're playing. Things like fret buzz can be a symptom of needing to visit a luthier to have your guitar adjusted.