I feel like I have this problem a lot actually. ^^ It sort of depends on what the audience needs to know about the story—will it be easier to give information in third person? or easier to hide information in first person?
In general, I prefer third person as I can explain more things than the character may be willing to divulge and for some reason it sounds more professional to me, but I'm pretty sure that's just my tastes and nothing more. ^_^