I have both the Apple Ipad 3 and the Android tablet(Thrive) and I like both of them. I cant see a bit of difference between them regarding the display quality, tho the Ipad is supposed to be twice the resolution.
Laid on the side, the Thrive is one inch wider, but one quarter inch lower in height. The big plus about the Android is that you can use it just like a PC as far as plugging in USB sticks and having easy access to your files and moving files from tablet to PC. Unfortunately, the instrument manufacturers have embraced the Apple and they are producing apps for the Apple, but not the Android.
I do not know about the latest Kindle tablet, but the earlier were very limited.
I have not yet seen any reviews of the Microsoft tablet - maybe it will be a good way to go.