Only iPads with 3G have a GPS
http://www.apple.com/ipad/specs/ ... this includes all generations of iPads and the new iPad mini.
GPS does work outside of 3G coverage (slower to initially determine you position, but otherwise all good). Note that using a WiFi-only iPad in the city may trick some into thinking it has a GPS as it uses crowd-sourced location information of WiFi routers to determine your position.
Some Android tablets come with inbuilt GPS, others don't.
I purchased one off AliExpress which stated it has a GPS, but it doesn't (damn shame, it's a great tablet, great screen, was only about $140, just a shame it doesn't have the GPS).