I've tried Fullscreen and Sleipnizer, and Sleipnizer is more flexible (it plugs into various other Cydia apps) and has lots more options.
I've read that Swipe Safari conflicts with Zephyr and causes PDFs opened in Safari to crash. Don't know if that situation has changed.
I've tried using other browsers like Mercury with built-in browsers, but think Safari on iOS 6 beats all of them for speed and stability (even when using the Nitrous tweak to allow the Nitro Javascript engine to be used by apps other than Safari).