GCP VMs are per-minute, with a minimum of 10 minutes (vs AWS' new minimum of 1 minute). Second resolution is nice, but I doubt it makes much difference in pricing for most workloads. https://cloud.google.com/compute/pricing#billingmodel
Azure's containers don't use a full VM-- they're more like AWS Lambda or other serverless frameworks, so they do per-second billing with no minimums.
I would disagree on no minimums and equivalency to lambda et al, as azure container instances charge a create fee (iirc its equivalent to 100 seconds of their minimum configuration) which sits on top of the per-second billing.
We don't mind per-minute billing on GCP, but would love to get the minimum down to 1 minute or even less. We have some tasks that finish under 4 minutes where scaling horizontally instead of vertically makes much more sense to us.
Azure's containers don't use a full VM-- they're more like AWS Lambda or other serverless frameworks, so they do per-second billing with no minimums.
Disclaimer: I work at Google on Container Engine.