Still debating it, and I realize Yamaha will be more reliable, but D/M aren't that unreliable either, right?
Yeah, I don't think they're quite as bad as the internet would have you believe. Personally I HAVE seen a higher failure rate of them perhaps thanks to their association with Onkyo and sharing sub-par quality parts, so I've seen the same problems on Onkyos, Denons, Pioneers, usually being bad HDMI boards, but I think they have that pretty well sorted out these days. Unfortunately it tarnished their reputation for a long time.
As you pointed out, they can be dimensionally smaller too, but that could be at the expense of thermals. Yamahas tend to run cooler than just about anything, which I'm sure lends itself to long term reliability. Why they run cooler is due to a variety of factors but they've always blown me away with how cool they run, even when you're really putting them through their paces. Many of the Denons/Onkyos/Pioneers I've worked on have run HOOOOOOT, so if you have them in a cabinet, plan on adding active cooling. Any time I saw a customer with one, I'd usually insist on adding a ventilation system of some sort. Especially measuring temps and seeing an impending core meltdown coming. Almost every total failure I'd see with these products was likely due to them being operated in an enclosed cabinet. Any time I added cooling, I never saw a problem, so that's my guess.
I say if you keep second guessing your Yamaha purchase, then just bite the bullet and give the Denon or Marantz a try. No matter what the results, you'll probably be most satisfied knowing that you made a seriously informed decision in the end! Even if you go back to the Yamaha.
I'm all for experimenting, so give it a whirl and post your results!