Q: I see some sets of guitar strings that have a wound G string, and others that have a plain G string. What's the difference?

A: Typically manufacturers will use a wound G string when the gauge gets too high to use a plain G string — as a plain string gets thicker, it also gets stiffer. The wound string will stay flexible to a higher gauge.

Tonally, a plain G will sound closer to the plain B and E strings in a set, while a wound G will sound closer to the other wound strings in the set (E, A, and D).

Which is best is purely a matter of personal preference. If you're going for a heavier string set, a wound G will probably work well for you. If you use lighter gauge sets, a plain G will work well.