Marantz and Denon are owned by the same company. You generally get more features at a certain price point with Denon, but Marantz gets the beefier guts. I haven't done a side-by-side comparison of Marantz + Denon AVRs, but I am thoroughly pleased with the sound from my Marantz.
Marantz vs. Yamaha, if customer satisfaction is any indication, you really can't go wrong with either. I prefer Audyssey room correction in Marantz units over the YPAO correction of Yamaha, simply because Audyssey is better documented and I know it works reasonably well.
Re: the SR5009, if you don't need HDMI 2.0 or wifi connectivity, you could save some money and get last year's SR5008.