[Marlan]

It almost always depends on the quality of the room for me.

If I'm at the Academy of Arts and Letters or Purchase recital hall in New York (my two favorite places to record in the NY area), I will almost certainly opt for omnidirectional microphones. My ear prefers the sound that spaced omni's provide.

Sometimes I will also place cardioid spot mics in key areas to bring out certain things my ear likes to hear.

That being said you can get stellar results with ORTF, but I find I prefer the slight directionality over omni's in less desirable acoustic spaces where I can add artificial reverb later. You definitely have more control in post when using an ORTF configuration in my opinion.

In extremely reverberant spaces like cathedrals, I will almost always go for ORTF as a main pair instead of omni's, but I will use omni flank mics (outriggers).