In reply to Ryan_ID:
I have climbed it as an expedition leader for one of the main UK providers, and we got all bar one of our 10 person team to the summit. (The one that didn't suffered from AMS, despite the below)
I believe this was due to an excellent acclimatisation regime that uses an extra day rather than tries to get up and down too quickly. We were also lucky with the weather, in that it wasn't too windy, and the snow cover was minimal.
We did the excellent Vacas valley route, then False Polish traverse, descending the Horcones. I would have hated to have just doen the up and down, as the Vacas approach is far more attractive, less busy,and gives a satisfying traverse with more variation. I would therefore recommend that. Plaza Argentina is waaayyy better than Plaza la Mulas.
We insisted on double boots, and they seemed superfluous due to the excellent conditions, but it could have swung the other way. It is only just under 7000m, and is often understimated as a 'walk', which of course it can be if all goes well.
But it is high. It was bloody cold. It was the hardest 'walk' I have ever done. It can be very stormy.
Porters/mules can be hired from Penitentes, but expect to pay handsomely. And check your rescue status if going unguided. You must get your permit, and check in with the camp doctors.
Just don't underestimate it.
Post edited at 15:38