Android: YouTube's app on Android has gotten better, but there are still some sweet features that you can't get. If you want sweet floating videos, but only want to use one app, Viral is the way to go.
This app replaces nearly all of the official YouTube app's functionality while adding several goodies. The most noteworthy is the ability to pop out a resizeable floating video player so you can watch something while multitasking. It also includes some more refined search options, the ability to manually adjust resolution (where the official app only allows you to alternate between HD and non-HD), and loads of settings to tweak.
Viral Pro [Google Play Store]