If you want only one ski and need it to perform in all conditions, then the exp is your ski. It will perform ok in all conditions, but won't be great at any. If you want the better on piste carver, then go with the 5 star. It won't be good in powder, but is great for carving up a mountain. My preference for an all mountain ski is the Dynastar Legend 8000. Performs great in a foot of powder and has fantastic edge grip on piste and ice.
Your best bet: demo if you can. If you are open to other skis, search this forum for past threads. There are great reviews that address the best all mountain ski question. Many believe the Atomic Metrons, I think the 8000, and the list goes on and on. If you are looking for all mountain, the 5 star won't be at the top of too many lists. There are also other threads that specifically address the strengths of the exp and the 5 star.