I have a 722 and a 612.  Note my 722 is not the k version.  I had the k but the guide was too slow and I sold it.
My 612 works pretty well flawlessly.  My 722 is the same and it has TV2 an PiP as mentioned.  I would vote the 722 as the best Dish receiver right now.  The 612 would come in second.