I have found Grafana to be a decent product, but Prom needs a better horizontally scalable solution. We use Vector and Clickhouse for logging and works really well.
All of them provide a way to scale monitoring to insane numbers. The difference is in architecture, maintainability and performance. But make your own choices here.
Before, I remember there was m3db from Uber. But the project seems pretty dead now.
And there was a Cortex project, mostly maintaned by GrafanaLabs. But at some point they forked Cortex and named it Mimir. And Cortex is now maintained by Amazon and, as I undersand, is powering Amazon Managed Prometheus. However, I would avoid using Cortex ecaxctly because it is now maintained by Amazon.
