As a singer, I do much better standing, and I believe the showmanship is better too. A background situation is fine for sitting...looks very musical and professional, but takes you down to the audience level....something I try to avoid when I'm on stage.
My approach is to feature myself, and be as visual as I am audible. Standing allows me to move and use body language to interact with the clients, and if you move enough, you won't get sore!
Sitting is actually much more stressfull for me than standing ... then again, I do have a small basketball in my lap at all times!
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