I buy everything, long as it's in the zigbee2mqtt library I'm good to go.

I use mostly Sonoff, Aqara and Ikea, but I have a variety of other brands as well.

Sonoff is cheap and reliable, a few of their sensors have a the odd quirk but have worked well overall.

Aqara have more features and a more elegant physical design, but can be bit more expensive - although still cheaper than some other brands. I have a lot of their temperature/humidty and contact sensors and they look nice on my walls and windows.

The one problem with Aqara devices is they don't properly follow the Zigbee standard, and don't play well with some other brands, leading to constant disconnections. They do work fine with Ikea devices however. I had a lot of problems until I split my Zigbee network into 2, one with only Aqara and Ikea devices, and one with all the rest.

I'm also using a few devices from Samotech and Aurora, who have some good UK specific Zigbee devices such as rotary dimmer switches and smart sockets.

I would use Shelly for relays, sonoff for sensors

I’ve had good luck with either Sonoff or Tuya. Look on Aliexpress for much cheaper options. Just make sure you get the Tuya Zigbee vs WiFi devices as they’re sometimes listed on the same item but just a different “color” option when ordering.

I use this with zigbee2mqtt

My zigbee network is predominantly Hue bulbs and fixtures. Not cheap but reliable and they come in a lot of form factors. I think the only other zigbee device I use is the kwikset convert. I didn't want a keypad on both of my doors so the convert was a cheap and easy solution