Definitely Safari. I've never gotten into "fullscreen mode" in any browser. Safari in Lion has changed my whole web browsing habit. It's just so smooth and perfect. YES! Leave the address bar up there! It takes up just a few pixels, but is so much more convenient. Plus, I've always hated how janky the disappearing address bar in Chrome and Firefox were. Move your cursor towards the top of the webpage, and everything gets screwed up. Plus, they both leave that scroll bar on the right hand side up, which drives the OCD in me insane when on a non-white webpage. I'm sure that will be fixed soon, as the aqua scroll bars are no longer in use.
The whole page transition thing is pretty amazing too. I just love how the page moves perfectly with your fingers when you swipe.