Describe what kind of site you're making. Will it be all static, will it have a blog with commenting, or a forum? Is it a personal, business, or some other type of site?
If you're just making a iWeb site, just go with the basic essentials and cheapest because it doesn't need much of anything. If you have dynamic content like a blog you'll want to make sure the host supports the languages you need such as PHP, which most do these days. As for a dedicated hosting IP, if you don't know if you need that, then you don't need it.