Amazon ELB is the more common of the two in our index: it runs on 400 websites against 206 for Google Cloud Load Balancing. Counts come from real scans, not vendor claims.
AWS ELB is a network load balancer service provided by Amazon Web Services for distributing traffic across multiple targets, such as Amazon EC2 instances, containers, IP addresses, and Lambda functions.
Google Cloud Load Balancing is a scalable, fully managed global load balancing service using Google Frontend.
Want to know which one a particular site uses? Look it up and see its whole stack, or compare two sites side by side.