I prefer the stock UI, which should be available for all phones. I don't have a Galaxy S phone, so I don't know if TouchWiz is available with any of the custom

I prefer the stock UI, which should be available for all phones. I don't have a Galaxy S phone, so I don't know if TouchWiz is available with any of the custom roms for them. Either way, that info should be on the xda-developers website.