.012-54's are the most popular and what comes shipped on most new guitars. It's our best selling string gauge for acoustic and it's a really good compromise between tone and playability.
If you want to torture your fingers, grab a diehard bluegrassers guitar and play it. Most those guys use AT LEAST .013-56's and have their action pretty high. The higher the action and heavier the string, the louder your acoustic guitar will be, as a general rule. Those guys don't plug in and they want to be heard so they string 'em heavy and leave the action high.