We've been a Google Cloud customer for close to a year now and just recently signed a deal to move all of our infrastructure over to them from AWS. I've previously managed infrastructure spends of $>10M a year on AWS before, so have a decent amount of experience with them. I've never used Azure.
We had been running our CI/CD pipelines on Google mostly because we received startup credits from them. Over time, our use cases expanded as we adopted BigQuery for data warehousing. We choose to commit to Google long term because we've been a heavy Kubernetes shop in got tired of managing it ourselves on Amazon. We participated in the Amazon EKS alpha and felt that they were years behind Google in their Kubernetes implementation. We have probably been able to save 1-2 DevOps hires this year by adopting some of Google's managed services.
If there is a downside on the technical side, it is that some of their products don't have the same number of features as Amazon such a prefix signing and reporting on GCS. There also isn't the same level of community awareness on how to use their stack so documentation gaps are more painful. Other things like a lack of presence in China could be challenging in the future as well.
On the business side, Google has been amazing to work with. Whenever we have a technical question, the sales team has generally been able to quickly get us an answer or we've got to talk to the product PM. When working with Amazon, you are usually referred to a solutions integrator who can't answer tough technical questions. Google is very open with early access releases as long as you're willing to provide them feedback - which they truly value. Their sales processes aren't as mature as that of an established enterprise company - which can be a good or a bad thing - but they've certainly earned our trust as an enterprise customer.
In some ways, any of the big 3 are going to have marks against them in some way as they just do too many things for them not to piss you off in some way. I wasn't a fan of Microsoft a decade ago because they regularly killed open source products I liked by releasing their own version of it under the Microsoft name.
When looking for partner I'm looking for someone who can accelerate my business and earn my trust. So far, that's what I've gotten from this relationship.