When you buy into zigbee, the most important thing you need do is this #1 and the rest in order:
1.Most important decision, is the zigbee gateway you go with. I personally prefer my sonoff gateway flashed to tasmota. Then you can set it in serial to tcp mode, use either ZHA (built-in HA) or zigbee2mqtt mode.
If you have an open gateway like in #1, the brand of zigbee devices really doesn't matter, you can mix them
2. Get as many routers as possible. I bought the sonoff zbasicr3 and then I added 3 pin plugs, and plugged them in to as many plugs around the gateway and house to extend the range of zigbee in the house. This is also very important, unless you stay in a small flat etc.
3. Now you get all your sensors, and really you can mix them. I have both sonoff and aqara temp/humidity sensors. I also have aqara buttons so that I can just press buttons in certain rooms to trigger a few manual automations. This is by far the biggest advantage of zigbee, the other being that their batteries last at least a year to 3 years and generally being smaller than the wifi versions.