Kubespray runs on bare metal and most clouds, using Ansible as its substrate for provisioning and orchestration. Kops performs the provisioning and orchestration itself, and as such is less flexible in deployment platforms. For people with familiarity with Ansible, existing Ansible deployments or the desire to run a Kubernetes cluster across multiple platforms, Kubespray is a good choice. Kops, however, is more tightly integrated with the unique features of the clouds it supports so it could be a better choice if you know that you will only be using one platform for the foreseeable future.
Kubeadm provides domain Knowledge of Kubernetes clusters' life cycle management, including self-hosted layouts, dynamic discovery services and so on. Had it belonged to the new operators world, it may have been named a "Kubernetes cluster operator". Kubespray however, does generic configuration management tasks from the "OS operators" ansible world, plus some initial K8s clustering (with networking plugins included) and control plane bootstrapping.
Kubespray has started using kubeadm internally for cluster creation since v2.3
in order to consume life cycle management domain knowledge from it
and offload generic OS configuration things from it, which hopefully benefits both sides.