There isn't a string gauge that is better than all the others. Depending on your taste and needs, some string sets might be a better option for you. Typically, .009 string sets aren't used a lot in acoustic guitars because you don't have a lot of string tension, which is nice to have on an acoustic guitar. However, a lighter string gauge might be easier to play as you develop calluses on your fingers if you are starting out. Generally, acoustic guitars work well with string gauges such as 11-52 or 12-54. If you plan to use alternative tunings in which you significantly drop the pitch of your strings, it is a great idea to get a heavier string gauge to compensate for the loss of tension.