Given that the double and the triple shift with equal reliability and that the high and low of the system are the same, measured in ratio or gear inches, the advantage of the triple over the double is narrower splits between the gears, because the same range is spread over more steps. If it matters to you, you can stay closer to the optimum cadence more often with a triple. If you want to ride with a pack of singles, it makes sense to gear like the singles, so I prefer to use 53-39-28 chainrings, and the smallest cassette I can get away with (11-21 is ideal) for the terrain of the day.