Typically you want to create a stereo image by using some sort of array ot two microphones. There all sorts of arrays:
Coincident - the heads of the two mics overlap. You probably want a matched pair of mics or two of the same model. A typical array is the X-Y 90' pair.
Near Coincident - the heads may be spaced a bit but the distance and anglel are calculated to give a nice sound and a decend mono compatibility. This option often yields a wider soundstage than the coincident pair but you want to find an array, such as the ORTF system (110' and 7" apart), that will yield predictible results. You probably want a matched pair of mics or two of the same model.
Spaced Pair - The mics may be set up as a cohesive spaced array or placed for two different sounds and then panned as desired.
I've listed them from the most mono-compatible to the least mono compatible. Why do you need mono compatibility in this high-tech world? Well, for instance, YouTube LoDef is mono. If your two channels of stereo don't combine well to mono, you often get
mush. This is especially true of the business of making two tracks and slipping one out of phase with the other.
Bob