and should I use a particular one of them?
You have no choice in the matter at all. Use this attribute in your script tags
I many time see Java Script error in the status bar of my browser for other sites, and I don't want to see that on my web site.
It is irritating, isn't it. Sun's Java website is currently throwing up "stack overflow" alerts. You'd think they'd know how to use a scripting language.
You can hide that nasty error triangle by including this small piece of code:
You can use the <noscript></noscript> tag to wrap html code that should only be applied if js is absent/disabled. However, you should be aware that whilst browsers are happy for <noscript> tags to appear in the <head> w3c validation will generate an error.