I've been to both places twice each. I loved them both, but I agree with the others, they are quite different. If you're into the ancient world, the Temple of Artemis (one of the Seven Wonders of the ancient world) was at Ephesus. Cappadocia is quite unique and I don't believe you can see anything similar anywhere else. Hard choice, but with limited time, Ephesus will be closer than Cappadocia.

sgreif,

I stayed in Istanbul at the Hotel Uyan in the Sultanahmet area last October. It's a cental location and the room was clean and staff was helpful. The room rate was under 100 Euro and included breakfast. Here is the website www.uyanhotel.com

I also think it's a tough call between Ephesus and Cappodocia, but if I had to recommend one over the other it would be Cappodocia and consider a hot air balloon ride, it was magical! :)