Wired or Wireless
This is another component in the chain that can make a big difference. As Chris mentioned previously in this thread, there's nothing worse than drops outs, hiss, crackles, etc that wireless systems can sometimes include. Our lead singer runs through a Sennheiser G3 wireless system and he likes it since he moves around a lot. It's very dependable and easy to setup. I also have the G3 system but I prefer the sound quality of running wired. I also own some cheaper wireless systems but we don't run them anymore because we just weren't happy with the sound quality compared to wired. If I had to run wireless, I'd plan on a $1,000 price tag for each user.