I use zigbee2mqtt myself and I’ve been very happy with it. I haven’t tried ZHA, but I believe z2m supports more devices. (I use z2m’s supported devices list to choose which ones to buy.) The downside is that it’s a bit more work to set up initially, as you need an MQTT broker as well. But in return, I feel like z2m is more reliable since it runs (and is updated) separate from HA core. I use it with a zzh! dongle and even though I got one of the bad ones with a faulty amplifier chip, it’s been rock solid.
As for Thread(+Matter), I’m waiting for things to settle down. Support in HA is still experimental and there are very few products out yet that use Thread. I’ll probably prefer Zigbee for as long as they sell them so all my devices will share the same mesh. Also, unlike Zigbee, Thread devices are not guaranteed to be local-only, which is my biggest worry. Thread/Matter won’t free us from having to check a device compatibility list before buying.
This is my impression as well. I’m keeping an eye on how this space develops and I’ll probably buy a second dongle just for Thread when I need it (i.e. when some product I really want comes out that only supports Thread.) I believe most zigbee dongles are theoretically capable of supporting Thread, since they both share the same physical layer protocol.
I’m curious to hear people’s experiences with Thread/Matter devices. Ideally, I’d like to use my HA box as the border router and configure it to not allow any external Internet connections. Will this break any functionality on devices with a Matter logo on them? Ideally it shouldn’t, but given the track record of manufacturers so far, my expectations are low.