IIRC the HK has more flexible bass management and a couple of extra surround modes for stereo content while the Marantz has a bit more power and probably has some other features I don't know about 'cause I don't own one
I don't think you can go wrong with either. I ended up with an HK (a couple of HKs actually) but probably could have been equally happy with the equivalent Marantz.
Do take a hard look at HK pricing though -- there are some fantastic deals available on the HK x30 models now that the x35 models are coming in, but for most of us the new models don't really add very much of interest. I picked up an HK 130 at FutureShop today for $299 CDN which is a really good price (HK is expensive in Canada). It's going to be the start of my brother-in-law's "high quality low budget" system.
