Moving your question to the vSAN forum...
I don't think there's best practice for Object space reservation (%). It totally depends on your requirement. If you want to preserve storage, thin is the way to go. Else go for thick. Either way, it all depends on VM sizing and requirement.
Some background into your current infrastructure (Physical server model, Disk group configuration, ESXi version, vSAN version, vSAN policies configured) and the requirement from which your current query stems from would be helpful here.