The Nexus tablets for me are the only real competitor to the iPad. The Samsung Galaxy series are good but you'll find side-by-side against the Nexus' that the 7" and 10" just don't perform anywhere near as well.
For those that tried Android tabs but haven't experienced the Nexus I suggest you have a play with them, they are a massive step up from the older Android tablets.
When I got my N7 I must admit I thought I would constantly wish I'd gotten the Nexus 10 instead, but after using it I quickly fell in love with the size of it, it's big enough that the screen is much more usable than my Galaxy S3 but it's small enough to fit in the inside pocket of my coat. I never find myself wishing for more screen area, except for watching movies (which I'd rather do on my TV) although I must admit when my best mate brings his N10 round that screen is just sublime! So god-damn sharp.
One thing I also like is that Android doesn't need separate apps for tablets to get the most out of them, as Android apps are developed to operate at many different resolutions, so for example the Sky Sports App looks just as sharp on my Nexus 7 as it does my Galaxy S3 or my wifes HTC One S, rather than a zoomed in, pixelated version.
What I don't like however is that a few (and it is only a few now) app developers don't treat Android as high a priority as iOS. Denon being one of them with their AVR Remote app which specifically pisses me off! Most app dev's nowadays are very good though even our golf simulator at work has an android app that works seamlessly and that's very niche.