They're different approaches to solving the same problem (improved throughput with lower latency and jitter). The major thing they have in common is that they both dedicate hardware to the problem.

With respect to AWS, in the historical "enhanced networking" case Amazon dedicated hardware by offering SR-IOV capable NICs. SR-IOV is a well understood and effective technique for approaching bare metal performance for virtualized environments, but it tends to lock you into a particular vendor, if not specific model, of hardware. I gather ENA does something a bit different, but I don't know the details.

In Google's case, we dedicate hardware to the Andromeda switch in the form of processor cores (the "SDN" block in the linked post). This allows us to be flexible in terms of NIC hardware while presenting a uniform virtual device to guests, in addition to simplifying universal rollout of new networking features to all zones/instance types.

Both approaches have tradeoffs, although I think even with ENA AWS hits ~70µs typical round-trip-times while GCE gets down to ~40µs. Amazon's largest VMs in some families do advertise higher bandwidth than GCE does currently.

(I was the tech lead for the hypervisor side of this launch — Jake, the post's author, leads the fast-path team for the Andromeda software switch)