While I have never done a same-day turn around in either city, if you have to pick one, I would suggest Accra. Lagos is simply not a nice city. Not much to do, not safe, utterly corrupt and you will be hassled as a foreigner. Accra, on the other hand, is quite the reverse. It's one of the nicer cities in Africa, and the people are very friendly.

If you find yourself short on time in Lagos, you will need a few well placed dollars to ease your passage through the airport.