What's the differences: omnidirectional vs. unidirectional microphones?
"Unidirectional" is just another way to say directional. It seems that a directional microphone is always better recommended than an omnidirectional one, thanks to its focus on one-direction sound and its phase-out of unwanted sound as a consequence. In fact, it’s a great choice when you are recording just one person’s voice and that needs your complete focus; however, it will not allow you to hear from another person on the other side unless you try to reposition the equipment. Neither microphone is “better” than the other - they just have different features and they both perform well in their situations.