To kind of threadjack, I have the same question, but I would like to know what is the best and simplest shotgun stereo mic that is easy to hike, travel, camp with?
Rode videomic or sennheiser mke400 are decent in expensive mics. For audio the rule is get as close as you can without the mic being in the shot, or ruining the shot. If it's camera mounted this means being very very close with the camera, or preferable, as I continually advocate... micing off camera. On camera is absolutely fine at a long push for run and gun. But if you are minded to sepend decent money on a mic, it implies you are (rightly) taking audio more seriously. To them cameramount with a lousy perspective and camera/handling/operator noises kind of puts you back to square one!
Or would it be best to get a general omni-mic that will record sound in most directions?
For general ambinece the built in mic is actually an ok omni pick up. Prone to wind rumble so google rycote micro-windjammer for a solution.