Hi Davis4,

First, your Martin guitar will have a lot to do with what kind of sound you get when you play it. (hooray for Martins!) The gauge and type of string will also have some effect, but primarily it's the guitar itself that will determine it's sound flavor. (that is, if the strings are "alive" and not "dead". Nothing sounds too great on dead strings).

In terms of the string gauge, let me ask you this: are you strumming, or playing fingerstyle, or some of both?

Unless someone is more of an athletic acoustic rock strummer, or hard-pickin' blues player, I tend to recommend light gauge strings.

It just so happens we're having a Strings discussion on my forum right now, with more info. Here's a link if you'd like to have a look:
http://www.guitartricks.com/forum/showthread.php?t=28622

Best wishes - Lisa