I think it really boils down to what the customer requirements are i.e. software/hardware VTEPs, scaling requirements etc. I've worked on a couple of scenarios that resulted in an NSX overlay within the virtualised infrastructure with a separate EVPN-VXLAN overlay in the physical network. NSX works well in VMware only environments and is pretty much fully integrated with vCenter. With regards to multiple sites, do you require L2 stretch between the sites or all L3? OVSDB with NSX is only used when integrating hardware VTEPs, or L2 bridging. I've never seen this deployed in production and the general feeling is to steer away from mixing hardware/software VTEPS. With regards to configuration, it's very unlikely that you would manually administer an EVPN overlay. Typically automation techniques and tools would be used.
Industry standard adopted by all major vendors.
Provides a clear demarcation between Network and infrastructure
With the use of EVPN as the control plane, hardware VTEP gateways can support different modes of redundancy such as All-Active or Single-Active multihoming.
Hardware VTEP gateways offer high-density, high-performance and better scale.
For larger deployments, if there are a large number of BMSs that need to communicate with the virtualized workloads, or if there is need to handle large traffic volumes, then a high throughput hardware gateway offers a better solution.
Based on the desired deployment requirements, hardware VTEP gateways can be used to provide physical-physical (BMS-BMS), virtual-virtual (VM-VM) or virtual-physical (VM-BMS) connectivity.
Centralised SDN based network overlay
Provides a logical network and security management plane, control plane and data plane functionality
Extends logical switch to support routing in the hypervisor (DLR)
NSX Edge can be for routing and for stateful services such as firewall and load balancing
VXLAN is used for transport networks
NSX controllers maintain and control the distribution of MAC / IP information to hosts
Does NOT natively support multi-tenancy. Requires 1 logical switch per tenant.
I would also suggest you take a look at Contrail as an alternative to NSX, as suggested by rccpgm
I hope this helps 🙂