After some intense google and SO search i couldn't find any document that mentions both rolling update and set image, and can stress the difference between the two.
Can anyone shed light? When would I rather use either of those?
EDIT: It's worth mentioning that i'm already working with deployments (rather than replication controller directly) and that I'm using yaml configuration files. It would also be nice to know if there's a way to perform any of those using configuration files rather than direct commands.
In older k8s versions the ReplicationController was the only resource to manage a group of replicated pods. To update the pods of a ReplicationController you use kubectl rolling-update.
Later, k8s introduced the Deployment which manages ReplicaSet resources. The Deployment could be updated via kubectl set image.
Working with Deployment resources (as you already do) is the preferred way. I guess the ReplicationController and its rolling-update command are mainly still there for backward compatibility.
UPDATE: As mentioned in the comments:
To update a Deployment I used kubectl patch as it could also change things like adding new env vars whereas kubectl set image is rather limited and can only change the image version. Also note, that patch can be applied to all k8s resources and is not restricted to be used with a Deployment.
Later, I shifted my deployment processes to use helm - a really neat and k8s native package management tool. Can highly recommend to have a look at it.