I just ordered and tested both the Sony WH-1000XM4 (XM4) and the Sennheiser MOMENTUM Wireless 3 (MW3). Both are good upgrades from my wired Sennheiser MOMENTUMs from 2012.
The XM4s have a better profile against your head; fewer protrusions and lower potential to knock them off or damage something else. They have better noise cancelling than the MW3s and are lighter too. The XM4s fold up more and pack in to a case about half the size of the MW3s.
Other than that I give the win to the MW3s. The ear-cups are larger and more spacious, ear pads larger and more comfortable. If you move your head or jaw too much with the XM4s the shifting will move your ear to block and significantly dampen the sound. That doesn’t happen with the MW3s, they sit more stable on your head even with a heavier weight. The MW3 build does feel nicer with the metal and materials quality.
MW3s have superior sound to my ear. The XM4s do a fine job, and push the mids/treble more for a lively fun sound. Great for rock or vocal fans. The MW3s seem to roll off the treble a bit more by comparison but they offer a deeper clearer bass and a bigger soundstage. Sounds have better separation and you can boost the mids/treble if you want with the Sennheiser Smart Control app.
Finally the XM4s fall down considerably in the on-device control department. They mostly use these barely responsive touch controls on a flat, unadorned surface. They were completely unreliable for me. Now a lot of us are used to limited control with AirPods and use phones/watches, but the controls need to be there sometimes. The MW3s have fairly easy to engage buttons on the rear of the right ear-cup. They have all the functions you’d want including multifunction play/pause/answer/hang up/battery info, voice assistant/pairing, volume, and noise cancelling on/off with transparency mode as well. Much better than the awful controls on the XM4s.
I’d highly recommend the Sennheiser MOMENTUM Wireless 3 headset if someone else is looking at this class of headphone. The are very capable and fully featured with sound that will compare well to AirPods Max, they come with a functional case and the cable accessories you would need. They will lack “Hey, Siri”, Spatial Audio, and automatic pairing, but the MW3s have simple Bluetooth pairing, automatic switching and multiple device support, noise cancelling and transparent modes, call audio routing with reasonable quality, and a very fast assistant/Siri button. They also have Alexa and Tile integration if you wanted to set those up. A good buy in my book.