All other things being equal--which they're not, and I'll get to that in a moment--if you want to record in stereo but for whatever reason you can't space the two microphones or microphone capsules more than a few inches apart, then directional microphones or a unitary "stereo microphone" would normally be the fairly obvious choice.
However, stealth recording may require you to keep the microphones or capsules very close to your body--and doing so fundamentally changes the way a microphone picks up sound since it obstructs all high- and upper-mid-frequency sound waves for least one major direction of arrival. In those conditions an omni is no longer omni and a cardioid is no longer cardioid, so any normal discussion of preferred patterns and setups no longer really applies; it's a separate realm.
One thing that might matter a lot is that pressure transducers (= typical single-pattern, single-diaphragm omni condensers) are FAR more resistant to handling noise or any other form of solid-borne sound than pressure-gradient transducers (= all directional microphones, as well as most switchable-pattern microphones even in their omni setting). I mean there could be a 20 dB difference in noise pickup. Same thing with wind noise, if that's a potential issue.
But if you're going to use omnis close to one another, you'll need some sort of acoustically opaque (dense) object between them (which could be your head or some other bodily structure of similar or larger size). Otherwise you'll be making a nearly mono recording. And even when microphones are classed as "omnidirectional," if they're of the usual size (e.g. 3/4" diameter) or larger, then they are directional at high frequencies, and should be aimed outward from center if they're being used within (say) a foot or two of each other for stereo recording.
--best regards