Functional difference between UMIG and ZONAL NEG IP and PORT

[amitbaid]

I would like to understand the functional difference between working of UMIG and Zonal NEG IP and PORT. I see them quite similar, 

• they can be added as backend to load balancer
• both of the types only support instance from a single AZ
• they do not support auto scaling
• except for NEG offering default port and port override feature, I am not coming across any major difference. 

I would also like to know when do I choose UMIG vs Zonal NEG IP and Port as backend for a load balancer.