I have have been using onRendered, to wait til Meteor has finished with a combination of various other things like Tracker.autorun, setTimeout and document.readyState. The problem is I find that this does not always work as a full proof solution with events firing to early.
For instance if I render an object to my template from a helper and then I would run a loop to apply a series of styles to the object that are now DOM nodes. But more often than the event fires early and the data comes later.
With Tracker.autorun it is not always a great solution because the events are not reactive data. document.readyState has the same issue as Tracker.autorun and is a bit more bloated in code than I want. And well setTimeout is just bad for UX in this instance because of the arbitrary wait time that is unnecessary to render the UI.
I have also tried attaching or tapping into values in the Template object, couldn’t come up with anything.