Film sets love lavs, and lavs are a great technology.
Lav mics are great for guerilla situations, handling multiple on-screen talents, etc.
But if you have a choice during editing to use a boom or a lav waveform...
I suggest going with the boom every time.
People often ask me why, so here's what I know from my limited experience:
- Booms are wired, lavs are wireless.
The wireless hop the signal makes weakens the signal, creating a weaker overall sound. Wired = better sound.
- Booms are directional, lavs are omni-directional.
The directional quality of the boom creates a richer, deeper sound - the wide-range of the omni-directional microphone could create a flatter sound.
- Lavs emphasize high frequencies.
Manufacturers know lavs are often hidden beneath clothing. Since hiding a microphone under layers of clothing could muffle the sound, the lavs are tuned to "cut through" the muffling by natively boosting its high frequencies. Booms are normally uninflected.
Lavs are great when you're in a pinch, or when the occasion requires a low-profile, or for capturing audio from a large number of people at once.
But if you could, side with the boom.