I have been a dealer of the following receiver brands on & off over the past 9 years:
H/K
Denon
Marantz
Onkyo
NAD
I've had extensive installation experience with:
Yamaha
Pioneer Elite
Without question, the Marantz products have been my personal favorite out of all of them and it's not even close! From the bottom to the top of the line it's been fabulous, sounds absolutely great, and has been nearly bullet proof (3 year warranty).
I like the fact that Marantz receivers are shallow. Marantz implemented this shallow chassis concept for, as another member posted above, in-cabinet use.
The reason it doesn’t weigh as much as an Onkyo, for example, is that Onkyo's design and amp implementation hasn't changed for a long time. Meaning: Old School. I was a dealer 99' - 2006/7 and can honestly say that the Onkyo product changed very little, if at all, engineering wise during that time period except for some new casing and video switching. They have to use large heat sinks and fans to cool their receivers because they get so darn HOT! Marantz uses a well ventilated copper plated chassis which cools their receivers naturally. They call this "Intelligent Cooling". So those big, heavy heat sinks and fans used in many other designs just aren't needed in a Marantz. I have seen the weight issue in regards to Marantz pop up on the forum before and just thought I would clarify why the traditional weight isn't there. Last years flagship THX Ultra2 SR9600 only weighed in at only 57lbs and that was an animal of a receiver.
Clint is right on about the set up woes of Pioneer receivers (Elite line included). To me, they're very very odd to deal with and not very smartly laid out. I think, though, that it's all about one's frame of reference. Personally, I've also had frustrations with Yamaha receivers as well but my issues are mainly linked to the video features they include. Everybody has their favorites, I guess.