Wireless Microphones are preferred by most KJ's and DJ's because they allow you to be anywhere without worrying about wires tangling. Wireless mic systems are not complicated but as with all things audio there are things you should know before buying. The entry level systems are usually VHF (very high frequency) and come in single antenna or dual antenna. The antenna on a dual antenna system are set half a wavelength apart (about 9 inches) and because of that one of the two is always receiving signal even when phase inverted reflected signals cause one antenna to dropout. Single antenna systems are ok if you are standing still but even small (one or two foot) movements can cause dropouts.
The next level of wireless microphone systems is UHF (Ultra High frequency). The main advantage of these systems is that UHF frequencies can be closer together so there are many more usable frequencies in the UHF band. The other thing to consider is durability and one button push frequency select. These features scan the UHF band for a clear channel and then send the selected frequency from the receiver to the transmitter. Really high end systems also show you the transmitter battery strength on the receiver.