I used Easy Taxi a few times in Lima, and it was pretty straightforward. The drivers have a book provided by the company that has fixed prices in it, so no haggling necessary if you don't speak Spanish. I would agree that it seemed like you paid 2-3 soles extra, but the cars were generally nicer than the few times we hailed a cab off the street.

Also, walking around Cuzco last night I saw a poster for Peruvian Shuttle. I have no experience with them, but their rates to Miraflores and San Isidro looked to be similar to Taxi Verde's walkup rates, and it might be slightly less time-consuming to pre-book instead of wait in line at the airport.