These two models are quite different and you need to keep in mind some features of these models to choose the one that will serve you perfectly. I have studied user reviews and features of both devices to help you choose the right option for you.
A huge range of functions including 9 channels of amplification, network broadcasting, a good combination with audio formats Ultra Hi-Res, Bluetooth, Airplay, Spotify Connect, TIDAL, Deezer for re-creating melodies from smartphones, and of course the unchanged technology of HEOS. Also enhanced features in a multi-edge spectrum with 11-channel processing and pre-generated outputs for all channels, RS232 Control and Crestron Connected.
The Audyssey speaker setup improves the sound quality. I love the Bluetooth feature; even Amazon music sounds great! Having an HDMI output for a Zone 2 TV is great. I am running 5.1 and Zone 2 & 3. Much improved GUI menus and de-complicated remote control are appreciated improvements. I was able to remove an HDMI splitter for zone 2 and a Bluetooth receiver.
AV receiver 9.2 with support for DTS: X, Dolby Atmos and HDR, 125 watts (8 ohms) per channel, Audyssey MultEQ XT32 auto-calibration system, 8 inputs and 3 HDMI outputs with 4K support, Bluetooth, USB. All eight HDMI inputs and three HDMI outputs support compatibility with HDCP 2.2 and the latest HDMI specifications and play 4K Ultra HD 60Hz video, supports high dynamic range (HDR), is compatible with Dolby Vision, supports Hybrid Log Gamma (HLG) and eARC (HDL) advanced sound return channel) for playing multi-channel surround sound from your Smart TV.
It is not that hard to choose the model you need. The first thing you should pay attention to is compatibility with modern formats.
Denon does not support AAC which is quite popular, plus it does not have Dolby surround decoder which is quite popular. Moreover, its power output is smaller (400 vs. 630 Watts). Nevertheless, it is a reliable model. If the power output is not that important for you and 400 is enough for you, then Denon is right for you.
Marantz SR7012 is an option for people who would like to feel the power of 630 Watts. Do not forget that Marantz SR7012 is more expensive than Denon.
Marantz SR7012 overview
Denon AVRX4400H overview
The best receiver is Marantz SR7012. Check Marantz SR7012 price at Amazon