I hate to be the one to say it, but in my experiences, I have not visited even ONE Magnolia showroom that impressed me and I've been to quite a few of them. Oh, they have some fantastic products all right, but I have yet to see them set up properly (or informed the customer of the fact that they're not EQd or whatever). They might show you one product (that they're pushing) that's calibrated and setup right and let you compare it another product that isn't calibrated at all. Really tough to do a proper A/B comparo with them. I can't tell you how many people I've heard complain that the SVS this or that sub just didn't impress them. Well, properly set up, most SVS will demolish much of the similarly priced competition. The problem was that the Magnolia store didn't have them calibrated for that sub and failed to take that into account. IME, I've noticed that BB salespeople LOOOOOOOOVE to push Klipsch products and completely ignore things like SVS and other good brands. Not knocking Klipsch or anything. Just saying that the chain sure seem to definitely prefer particular brands as a whole.
Now I understand that it's really really difficult to have total room EQ set up for every single combination of AVR, loudspeaker, and sub. Heck, I don't even know how possible it is. Thus, the reason why home auditions are so, so vital to many of us. A loudspeaker or sub might not sound great at the store, but could absolutely sing in your particular space. And vice versa.
Anyway, back to your real question. They're BOTH most excellent. I absolutely love Marantz products, but I've also come away equally as impressed with anything from the Aventage line. Either way, you'll get good clean sound. Yamahas are kind of known for being totally bullet proof. To me, I just love the Marantz aesthetics and overall design. Not sure how much of the "warmness" is placebo or genuine though. Could be for real, but either way they both sound fantastic. You just can't go wrong either way. As said above, examine their respective feature sets and go from their. For example, many people prefer one EQ software form over the other.
