I just (2 days ago) received the N7 16 GB tablet. Compared to older tablets it is the first one that I would consider to be a serious contender, if not altogether better than the iPad. JB is smoother than ICS (I also have the Samsung GSIII) but, because it lacks flash support has its own downside.
I'm sure that the 10" form factor has its uses, but the 7" screen of the SGIII is much more comfortable to hold withone hand to watch video and/or websurf.
I looked at the Fire HD before settling on the N7, and rejected it because of the form factor (it isn't comfortable to hold in one hand) and the conscription to the Amazon eco-system under a heavily modded ICS.
While I am not enamoured of Google Play, it is more open than either Amazon or ios. The fact that much of Amazon's content can be played on the N7, while the Fire HD has difficulties with native android apps is another reason that I think that the N7 is the major challenger to the iPad.
It would have been ni8ce to see Samsung offer a better, more competative, tablet. From this review it looks like Samsung put out the Tab2 as a stop-gap, and not a real competator.