So there's a Dutch website where people can log their fuel consumption. This s real life, normal people, fuel consumption. I just checked some modern cars, although with a small sample size, and manual transmissions seem to be more fuel efficient. Caveat may be that in the Netherlands an automatic is deemed a luxury and is therefore more often found on cars with bigger engines.

Here's the site: http://www.autoweek.nl/verbruiksmonitor