I've found the Facebook app on my GNex is faster than it was on my iPhone 4, but that might be chalked up to phone speed differences rather than the Android app actually being better.
Android WebViews still get to use full-on V8 (where the equivalent Nitro on iOS is limited outside Safari); which likely helps web-based apps on Android.
Despite that, the Android FB app, and most other WebView-based apps on both platforms, tend (IMHO) to be rather dog-slow and buggy anyway. The App Store in iOS6 is one as well, and it shows.