Personally, I currently use two CC2652 based USB adapters (one Sonoff Plus USB dongle and one ZZH USB dongle right now) to the same Home Assistant instance myself at home in order to utilize both the ZHA integration and Zigbee2MQTT for different Zigbee devices, (so one dedicated USB dongle per Zigbee platform, with both connected to the same computer with Home Assistant OS).
I primarily use the ZHA integration for the majority of my Zigbee devices because its component is natively integrated into Home Assistant (so do not have to deal with MQTT for it) and only use Zigbee2MQTT for a couple of newer non-standard devices that do not have full support in ZHA yet.
One of the main downsides with using both solutions at the same time is that I need to have a baseline of at least a few Zigbee Router devices in both of those totally separate Zigbee networks/meshes.
I think because Zigbee2MQTT still has a larger/broader community it does tend to get faster support for less common and odd niche Zigbee devices that deviate further from Zigbee standard specifications and therefore needing custom quirks/converter code for each individual device and function/attributes.
By the way, If you can code/script and prefer Python over JavaScript/TypeScript then suggest you use ZHA instead of Zigbee2MQTT, and vice versa, that way you can at least edit your own quirks/converters and contribute them back to the community, but if you can not code/script then suggest that you try out both, even at the same time (which again will require you to buy an additional Zigbee Coordinator adapter).
I actually started out my smart home journey with Z-Wave myself almost 10-years ago and today still have more “Z-Wave Plus” devices than Zigbee devices since most my Z-Wave devices still work great.
Z-Wave devices are relatively much more expensive however in my experience their build quality is generally great, and since Z-Wave specification has stricter certification standards their interoperability and compatibility is usually excellent, plus operating on the ISM radio band frequencies their lower frequency allow much better wall penetration and range, so it is easier to start out with a small setup.
What I like more about Zigbee is the very low price of most devices that enable a much wider adoption.
I personally believe that the new “Matter” (“Matter over Thread” and “Matter over WiFi”) standard is the future and my guess that given the time span of maybe 10 years from now it will eventually have out-competed all others existing standards as a choice when companies bring brand new products on the market as prices for those products drop because of competition, but think it will take many years before there is a large selection of devices at a similarly low price point available, so both Zigbee and Z-Wave still got quite a few more years before getting obsolete, (and your already bought devices will, of course, keep working in Home Assistant unless their hardware break).
Considering that being a brand new standard and Matter also requiring stricter certification to achieve better interoperability/compatibility (similar to Z-Wave Plus), I assume that most first-to-market “Matter over Thread” products will probably not be cheap as Zigbee devices, at least not the next few years.
Since Matter of Thread currently also only operate over the 2.4GHz band and not (yet) over lower frequencies like the ISM radio band it will also have the same wall penetration issues as Zigbee, but unlike Zigbee which is limited to only one Zigbee Coordinator I understand that with “Matter over Thread” will be possible to add more than one “Thread Border Router” devices and support fail-over by default to possibly remove that single-point-of-failure.
and came to the same conclusions 