Hi Sam Davidson,
This is a hard question to answer without knowing your specific requirements.
Have you looked at ZigBee.org
or the Thread Group
? Do you know what Ecosystem that you are interested in?
If you are serious about ZigBee and have the resources to invest we always recommend SiLabs EM3Mx-DEV(-IAR) Kits
(full disclaimer, they come with CEL ZICM35xSPx Mini Modules).