We use ArgoCD but almost went with Flux. However, it was partially due to timing. At the time Flux v1 was on the way out but v2 wasn’t quite ready for prime time, and we didn’t want to build everything in v1 and have then almost immediately migrate. However, over time we’ve come to think Argo was the right solution for us anyway, and we’ve started using other things from the Argo ecosystem like Events and Workflows.
Helm is really the basis of our ArgoCD apps though, but Kustomize is also part of the mix, basically how we deploy the same app into different environments