Hi John, we have no problem driving in Ecuador, although getting out of the cities can be a bit harrowing. And while I’m sure you wouldn’t, do don’t drive at night — the roads aren’t as well-lit as we are used to and in the mountains you’ll have fog at night which will make it difficult to see. All the major rental companies are in Ecuador. There is also one called Simon — Google it. I’ve not used it, but you might get a better rate.
An option is to hire a driver (expect to pay about $10 an hour with the understanding that he’ll have to return to Quito, for instance, if he drives you from there to Cuenca). Or if you travel light, you can take the buses.