I would choose one you like and can identify with. People who answer you are going to use your forum name in their responses, so you will see it often. It helps if you like it then. I have a history with mine, so it was a no brainer to choose it. Still if I did have to choose another, I'd think long and hard. If another user already has the name I like, I'd add a number to the end of it, or a period like Megan.
Bari Jo