If you want the quick answer to what UAV you should get... here it is: Get a Phantom (the older version DJI is still selling will work as long as you stay away from the P3 Standard!). Yuunec and 3DR don't have a get community of 3rd party apps to use and/or they don't geotag photos out of the box. If you're on a budget, get the Phantom 3 Advanced. If you want to have more flexibility and greater detail, get an Inspire. If you want slightly more power / more features, by all means, the Phantom 4 is a great pick, but for mapping it isn't doing a whole lot more than the Phantom 3 Professional.
The things you'd ideally want:
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