For me the connection between hue bulbs and xiaomi sensors works very well.
Yes, the ConBee supports transition.
Regarding ZigBee2MQTT vs. DeConz, I think they are both on approx. the same level at the moment. I don’t think you can say one is more stable than the other. Read up on both and decide for yourself.
Also check out this discussion on this topic: https://www.reddit.com/r/homeassistant/comments/akyr55/zigbee2mqtt_cc2531_vs_raspbee_premium_zigbee_addon/
thanks 
Yes you can use transitions with deconz. I have Hue, Osram, Müller Licht and IKEA bulbs and they all work with transition commands to fade lights on/off.
Very nice and very important
-Does zigbee2mqtt support Hue transition (fade)?
-When I look at the compatibilty lists of both systems a lot more products for Hue and Xiaomi are supported by zigbee2mqtt. Gledopto controllers doesn´t even seem supported by Conbee.
I think with zigbee2mqtt you can also add unsupported devices yourself, which is not possible with Deconz as far as I know. Do you happen to have one of the devices, which is not supported by Deconz? You can always ask the developers and maybe even help them to add a new device.
yes I have a Gledopto and a Lightsolutions RGBW controllers, xiaomi Water leak sensors, smoke detectors, vibration sensors, a cube and newer Philips Hue lamps and they are not listed on the Conbee supported list.
Do you know if zigbee2mqtt supports Hue transitions?
At the moment I use Mosquitto MQTT broker for all my Sonoffs. Can the same broker also be used for zigbee2mqtt?
Yes you can use the same broker for your Sonoffs and zigbee2mqtt. If you have so many unsupported devices, it may be better to go the zigbee2mqtt route.
Sorry. No idea.
Did you check out this page? I think the supported device list is more up to date.
I see the vibration sensor, leak sensor and cube are supported. Which Philips Hue lamps do you mean?
I would suggest to wait a bit. There are going to be new devices for zigbee2mqtt which have better specs than the current 2530 and 2530 modules.
I have not seen this list before but the smoke detector is not listed. I have some lightstrips, lightstrips plus and their new outdoor strip.
On this list I see no lights. Is there an updated list for lights too?
I see that there is a 2540. Is this a replacement and better one?
CC1352 and CC2652 are the new devices which hopefully get zigbee2mqtt support in the near future.
Okay I Will keep an eye on these devices. Thanks
Somome already made a request to add this smoke detector a few days ago.
I haven’t found any list of supported lights, I think it’s best if you ask here:
thanks for the information
Hey, have you got tradfri lights from IKEA?
Bc i have HA + Conbee ii and IKEA lights, but that transition thing is not working with any lamp.