More than anything else, it depends on which pattern sounds best to you! Cardioid may be the best choice for live performance but not necessarily for recording. In the studio (such as it is) I can actually get better isolation by using figure 8, as it has better rejection of sound from the side than a typical cardioid. I just point the back toward a spot where it won't pick up noise -- like a corner, preferably with some sound-deadening material in it. Or a closet full of clothes!

the Insolent Lad
Enough small empty boxes thrown into a big empty box fill it full. ~Carl Sandburg