I agree with John, and would add that I would almost always use Omnis.
Like with Lavs, Cardioid often seems like a great idea, but in practice makes positioning a challenge. Lavs can be managed, especially if you put them just a little further down the tie/shirt/jacket/whetever than you would normally, so as to give yourself a bit more leeway on head movement causing the speaker to move out of the pickup pattern. But with headsets, the slightest move can cause a really drastic reduction in level.
So 9 times out of 10, I use omni Lavs & headsets. Provided you are sensible with PA positioning, mic positioning, and keeping a quiet stage, I never have any issues.