I have flown all three airlines but only KLM to Tanzania. TK in comfort economy (LAX-IST) and business (IST-JRO) or economy is a better deal than comfort economy in KLM. Comfort Economy in KLM is almost the same as regular economy, but a tiny bit more legroom. Ethiopian doesn't offer PE and is standard economy seats and service. Check if your layover in IST allows you to take advantage of a free night or the city tour.