If you're looking for a job, AWS has the largest market share (33%), followed by Azure (19%), and GCP (9%).
If you're looking for a place to host your product, you probably can't go wrong with either of the three, but there are some minor considerations...
Personally, I would consider GCP a little more risky long term. There was a report last year about Google considering existing the cloud business and setting a goal to be a top two player by 2023. Since this seems unlikely, what then? Google has some anti-trust concerns, but the bigger anti-trust concern is probably Amazon. There is a non-zero chance that AWS gets split out from Amazon at some point.
Finally, I don't really know GCP that well, but it's my understanding it's a little easier to manage for smaller teams. I believe AWS is considered IAAS while GCP is more PAAS (although the lines get blurred depending on product). In my experience, for companies using AWS... having a DevOps team that smooths over the rough edges of AWS and provides tooling on top of AWS warts has been a requirement.
I have no experience with Azure, but I can't see Google out performing Microsoft in any world as long as MSFT has .NET stack.