What is the best handheld gaming system and what are the best games for it?

The 'Nvidia Project Shield'-It's a handheld gaming console based on
Android OS.It will be releasing on June 27 priced at $299 .It will have Nvidia's
'Tegra 4' processor(the fastest processor for mobile phones at present) and it can play Android and PC games..

You really need to get PS Vita. It is so awesome!!

http://www.amazon.com/PlayStation-Vita-WiFi/dp/B003O6EATE/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&tag=informazcom-20

The price has been dropped recently and so many good exclusive games are gonna release this christmas.