Frankly they are all great skis with very similar dimensions. This is how I would decide, maybe it will help you:
I am not a big Salomon fan and I think the Foils look like an Abercrombie or Old Navy shirt, but they are a great all-mountain ski if you are mid-weight. A heavier skier might overpower these a bit, and as in my case I weigh 195 lbs so I want something I can be really aggressive with. The Foils are out.
The PEs are a great all around ski if you like a stiff ski. They are solid in all conditions. I feel they have less pop and energy than the AR6 (obviously I haven't ridden the AR6, but I can speculate based on 4 pairs of Armadas I have owned). If price is an issue though, the PEs are a great choice.
My pick would be the AR6 because it is stiff with good pop and I have loved my Armadas in the past. They are slightly more expensive than the PE, but I personally feel it is worth it. (this is based on my AR5 experience).