It makes sense comparing Marantz SR5012 vs Onkyo TX-8020 because they both are able to give some premium features.
A significant difference between the receivers in the number of channels, Marantz SR5012 has 7.2 versus 2.0 for Onkyo TX-8020. Regarding power, then SR5012 has such a W/Ohm ratio - 100/8 when TX-8020 has a power of 90/6. The THD is 0.08% for the SR5012 but 0.03% for the TX-8020.
Competitors' digital to analog converter (DAC) is identical to 192 KHz/24-bit. Only the SR5012 supports Bi-amping feature. Each of the AV receivers can transmit an audio signal directly to the amplifier and bypasses any DSP processing. Only the SR5012 has Bluetooth support. The Marantz SR5012 has support for AirPlay, AirPlay 2, and its competitor in our comparison - AirPlay. Only the SR5012 supports Spotify.
Only the Marantz SR5012 has support for High dynamic range (HDR). Only the SR5012 provides HDMI signal transmission in standby mode. The SR5012 can scale the input HDMI signal, unlike the TX-8020. Dolby Vision technology found support only on the SR5012. Only the SR5012 supports HDMI Audio Return Channel (ARC). Unfortunately, HDMI eARC is not available on monitored devices. Of the two receivers in our comparison, HDMI CEC is present in only the SR5012. The TX-8020 has a built-in phono stage for connecting a vinyl player. An ECO mode is only available for the SR5012. The setup assistant will help you configure Marantz SR5012.
Only the SR5012 has a Dolby Atmos multichannel audio format support. A surround technology DTS:X is supported only by the SR5012.
The Marantz SR5012 is better receiver in this comparison. Check Marantz SR5012 price