If you care about reading books on your tablet, particularly in the open .epub format, I'd recommend
this review from the Project Gutenberg webmaster on the Kindle Fire (to summarize, he or she doesn't like it, and recommends the Google Nexus 7 instead).
If you're going Android, get a Google product (the Nexus 7) or the newest Samsung Galaxy-whatever series.
Anything less will be a craptacular disappointment as Android isn't well supported for updating firmwares.
basically, you can't go wrong with those devices, compared to all others on the market.
The Kindle Fire might be a nice alternative (and it is coming from a major player).
I like my iPad 1 just fine (though its getting a bit old, it shows that the core product is sufficient). Numbers is what I use to manage my character sheet (spreadsheet app). I use the built-in PDF reader for reading PDF rulebooks, and the web browser for d20SRD.org for rules.
Generically, I recommend the Nexus 7 for folks wanting Android, and iPad for those wanting to spend a bit more. Namely because, unless you are a tech head (who already knows what they want and why they need it), you don't need to go outside either of those 2 products to be happy*.
*obviously, somebody with a specific situation and need in mind gets my attention to consider what will best suit them. Most people aren't in that boat.