Epochs may not be instantly readable, but they do force everyone onto the same page.
In any case, I tend to view a timezone as a separate piece of data than the actual moment in time (but I know others have a different paradigm): datetime = accurate moment in time; timezone = the timezone for which this should be viewed, or was captured or, etc.
http://pubs.opengroup.org/onlinepubs/009695399/basedefs/xbd_...
I would go for UTC, since that is what 99.99% of the people think of (and so few even know about TAI, except for the smart ones like @jameshart! :-) )