Looking for directions between my house and the Boston airport shows a
surprising degree of variation between map services. Check this out:

Route Google Maps Yahoo Maps Mapquest
home to BOS 7.6mi, 12min 7.5mi, 16min 10.5mi, 19min
verdict optimal route, timing should be ~15min same route as Google, fewere pointless "continue on" directions ridiculous, and "avoid highways" option does not help
BOS to home 10mi, 16min 8.6mi, 19min 10.3mi, 18min
verdict possibly silly use of highway slow, stoplight-ridden trek through Cambridge optimal until entering Somerville, then just as ridiculous

This is a tricky example. As the crow flies, the Boston airport is rather
close to my house— probably 6 miles. The airport is in East Boston,
which is accessible via underwater tunnels from downtown Boston (there is a
bridge from Chelsea but that's far out of the way). There are at least two
different possible tunnels to East Boston, each of which connects to a
different highway out of downtown (I-93 or I-90), neither of which is
especially convenient to my place. There is also the option of exiting the
tunnels onto a fast non-interstate road (Storrow Dr.), which is scenic but
not direct, or to drive on city streets, which is geographically direct but
involves slower traffic and more stoplights. On top of this, while I'm
fairly confident the Yahoo/Google route to the airport is optimal,
I'm not sure how reversible this route is because the tunnel away
from the airport is not exactly adjacent to the one coming in.

In other words, the mapping services disagree on the return path, but so
do I— I've taken at least 3 different, reasonable paths home as well
as getting lost a few times. Times have ranged from 18 minutes to over 30
(with a jaunt through the industrial areas of Medford; whoops).

I wonder, is the route to my house from Logan Airport just a damned
tricky route to optimize? Or are the different services needlessly stupid
and divergent?