Anyone tried both?

Little comparison. The Fire is basically a whizzy ereader and a portal to buy stuff from Amazon.
An iPad is a computer that can be used creatively; try finding apps for a Fire that allow it to be used as a Korg Synth, a 3D CAD device, for drawing and painting…
They are both tablet devices, that’s it, really.

Nexus 7.?

All depends on what you want. They are both based on a consumption tax so the maker receives their money via what you spend on it. They are both locked into their ecosystems to different amounts. All the things cz lists are great if you want to use it for them. If you want a media consumption device the fire looks fairly good. Having had a play with the nexus 7 yesterday I liked it a lot especially at the size. The nexus 10 got a good write up on the register yesterday coming out better that the iPad for movies etc.

Apples app store is what people go on about but if you don’t use them it’s not much of a plus.