The ULTRA being narrower is a lot more comfortable to hold, just like my Nexus 7. It's my one big complaint about my retina mini, by choosing to make it the size Apple decided on, it's cumbersome even without a case. The edges of the mini on the front side are sharp and difficult to put up with.
Conversely the nicely rounded soft touch material of the Nexus 7 makes it extremely comfortable to hold one handed. Likewise the Ultra is also ergonomically superior to the mini. Although not retina, the Sony's display is gorgeous. A bit too big to carry as a smartphone, it's no match for my Note 3. Yet it's an enjoyable alternative just for fun.