Should you record your dialogue audio in mono, stereo, or surround?
Short answer: Record dialogue in mono to save yourself a lot of headaches. You can still use a lavalier and a boom for each person, but in your final mix, generally just use one or the other mic (i.e., use the lavalier as the backup just in case the boom track has a problem for that particular dialogue line).
Why record mono? Phase issues are much more likely to arise in stereo and surround recordings. This can result in constructive or destructive interference - comb filtering. It doesn't sound good.
Huh? Are you serious? What about every movie that has been produced in stereo or surround in the last several decades? They actually record 99% of the dialogue in mono and then mix that into the overall stereo or surround mix. And in most cases, they mix the dialogue to the center front speaker in a surround mix or equally to both speakers (center) on a stereo mix.
Links for the articles we looked at on constructive and destructive interference as well as comb filtering: