For me, it also depends on the mood. Some days I have a thirst for speed and others just a lazy loop or two is dandy. So you need several models! I've never actually owned a model long enough (or had one survive long enough) to consider it mastered. I have a problem with vertical and horizontal rolling circles generally, and one model I had that was good at those (the model, not me) ended up being dorked when I tried to recover at eye-level from an inverted limbo pass. poof.

You can learn a lot with a predictable model, but you can learn more with an unpredictable one.

If you have mastered the bunny slope you can either stay there and brag you never fall while skiing . . . or you can take a different lift to a steeper slope and keep learning. ;-) I t doesn't matter which path you chose so long as you keep moving.