As a user I don't have any strong preference either way but the presence of a shiny icon on my home screen prompts me to visit a site more often than a bookmark that is several taps away. Adding bookmarks to the home screen on the iPhone is more realistic with folders to organize them in but it's still a multi-step process to put it there in the first place. It's unfortunate tapping a piece of glass more than once is a barrier but it just seems to work out that way these days for me.