Use a Wireless Remote Microphone
I own my own microphones. Both of them are cordless. I’ve got both a hand-held and a lavaliere mike. If you do a lot of seminars, it’s a good idea to own your own mikes. This gives you control over your most important instrument as a speaker.
I prefer the cordless mikes because of the freedom of movement they allow. The only downside to a cordless mike is the occasional interference you’ll pick up. You can eliminate most of this by getting a “true diversity” mike.
Hand-held mikes are the way to go in my opinion. Although a lavaliere mike will make it easier for you to work an overhead at the same time, a hand-held gives you the ability to create a lot more vocal variety. How many singers have you seen that used anything other than a hand-held mike? The reason for this is that they can move the mike closer or further away from their mouths for effect.
The only singers you’ll see these days who use those space age looking headsets are those who do a lot of jumping around as part of their act.
Go with a hand held, remote mike!