Jonathan:
El Altar can be be soggy, but a great goal. There's no hut so you'll probably have the place to yourself. The hassle with El Altar is that you have to go through private property to access it, and they're pretty adamant about not allowing passage without the proper permission. The guide services have this taken care of, and you could probably find out the appropriate channel to do this, but as with most things in Ecuador it helps to have a connection. Look up Eduardo Agama in Quito, or type Cotopaxi Cara Sur in your search engine. He's a veteran independent guide who operates a recently opened climbers hostel/high camp on the South Face, which is a vast improvement over the goat-rope at the hut on the main route. Enjoy Ecuador!