UPDATE Oct 2017: We now usually use both a lapel and a handheld wireless mics for the ceremony. Both have their strengths, so when possible we use both to provide the best coverage and best possible sound.
Original Blog (2016): When it comes to the ceremony portion of the wedding, the question is often 'should we use a lapel microphone or a handheld wireless microphone?'. The answer isn't always so simple, as there are some things to consider. I spent many years as a Soundman/ AV tech before becoming a DJ, and have years of practice with audio equipment and sound. When it comes to wireless microphones, I usually recommend a handheld wireless microphone placed on a high quality boom stand, and the reason is mainly because the sound is usually slightly clearer, and there is a time factor advantage as well.
When using a lapel microphone, we attach the lapel mic to the officiant's tie and the transmitter to his belt. This of course can take some time and requires us to spend time with the officiant prior to the start time (not always possible). Another factor I have run into is the officiant's beard, as well as strong wind levels can rustle and affect the quality of the audio. One other factor is that since the lapel is static (as in placed in a fixed position), there is no opportunity to angle the mic closer towards the couple. This isn't usually too much of an issue, but sometimes a bride or groom will be extremely soft spoken and all the signal boosting available can't always compensate for that. However, when the officiant is 'beardless', the location is wind-free, and the bride and groom are all speaking at standard volumes, the lapel microphone sounds excellent and does a good job at picking up all three voices.
In most cases I find the handheld wireless microphone sounds excellent, and can be adjusted to pick up a faint talker. My suggestion is unless there is a need to have no microphone in the background of the ceremony pictures, the handheld wireless has a slight advantage.