This is just my opinion of course, but I have a nexus 7 and a 'normal' kindle with a keyboard* and I find the nexus great for browsing the net, watching videos, playing games etc. I won't read as such on it though, not books, as my eyes get strained. Sure you can use them in the dark, thats great, but when I read I prefer the lamp on and something that 'feels' like a book. To me the perfect combination is to have a full blown android tablet and keep the old kindle too. There is nothing to stop you installing the
kindle app on any android device, so you can still read your books (I assume!) should you wish to, but don't bin the old kindle yet.
And if you are going for an android tablet get the nexus, its more powerful than the kindle one for the same price. Unless you need the amazon kindle interface, which lets face it is mainly designed to tie you to their own store and as such has more limited app choices, you'd be better off without. Plus you have to pay $15 to remove the ads from your lock screen with amazon!
* Well, I don't really own them, but I have permanent access to them!