There are many receiver brands that integrate very well with Roomie, so it is difficult to pin one down as the best. That answer was much easier in 2011 when some of the receiver brands really were not up to par with regards to IP control. These days with 2012 or 2013 models, basically everybody finally has their IP control working reliably.
The only part of that question we can answer really is which receiver, of those we have tested from the 2012 models, provides the most functionality with Roomie. That is a very close call between the high end Denon systems and high end Onkyo. In this case we would give the edge to the <a class="alink" href="http://www.amazon.com/gp/product/B00829USKS/ref=as_li_ss_tl?ie=UTF8&tag=cyphersoft-20&linkCode=as2&camp=217145&creative=399373&creativeASIN=B00829USKS" target="_blank" rel="nofollow">Denon AVR-3313</a>. Because it supports both album art as well as full feedback in every category, and on top of that has a mode in which multiple iOS devices can connect simultaneously via IP, we think that's the best model from 2012 by a hair.
For 2013, the <a class="alink" href="http://www.amazon.com/gp/product/B00CALM17C/ref=as_li_ss_tl?ie=UTF8&tag=cyphersoft-20&linkCode=as2&camp=217145&creative=399373&creativeASIN=B00CALM17C" target="_blank" rel="nofollow">Denon AVR-X4000</a> is the most promising model so far. We would expect that Denon may introduce additional 2013 models.
Note that again many receivers are great choices. We also use Yamaha quite often. The only real gap there is that they don't offer Album Art, but everything else works great and they also have a multi-connection mode we added support for in 1.8.0. The majority of their 2013 lineup has not yet been introduced.
Thank you.