The PS Vita and Wii U Gamepad have the advantage of having the screen constantly in same place: between your hands.
Wii U Gamepad have the advantage of the fact that each console will have at least 1 gamepad with it, with the option of adding a 2nd.
the PS Vita is a dedicated handheld gaming console, the user could always play games on it even when s/he is away from the PS3/4. It can still use remote play on it even if you are away from the home console. Plus, you could have a wireless LAN party with it :-)
SmartGlass is a good concept for when watching movies, but games? you will have to keep track of a 2nd device and hopefully that device will still have the screen active when you look at it!
While the Xbox 360 and PS3 do compete against each other, Microsoft have nothing to compete against the PS Vita; and from their leaked future plans, they don't plan to release a dedicated handheld console. Keeping this in mind, it might be a good idea for Microsoft to release this application (app if you will) on the PS Vita as well!