Go here to compare, has ratings and most vehicles have actuals posted
(I've posted for two, Tacoma is one of them)

http://www.fueleconomy.gov/

Tacoma has the best MPG/power rating.  If you don't need the power (no
towing or carrying heavy loads) you can do better.  If not, you can't.

I traded a v6 Dakota (which I liked in every other way) because I
could not tow enough.  The V6 Tacoma I replaced it with gets better
mileage and is rated to tow twenty percent more.

Frank

You're comparing differently configured trucks.  

The Silverado Crew cab with a 5.3 with 4WD is 14/19, the base Toyota
I4 automatic is 19/25.  See how meaningless that is?

Pick a specific configuration, and go from there.

I drive several Silverados and one F150 on a regular basis, and
greatly prefer the Tacoma's driveability and smaller size.  The
current Tacoma is mid-sized (4000+ pounds), more like the Dakota, and
much bigger than a Ranger.  I don't want a double cab and don't have
kids, so the Access cab's size is great for me.  I can own any truck I
want, and I don't want a bigger truck.    

The owner of the F150 I drive on a regular basis also drives my Tacoma
on a regular basis.  We co-own an airplane, and often swap vehicles so
the correct vehicle will be left at the proper airport, as we move the
plane from base to base.  He's decided to replace his F150 with a new
Tacoma after significant time driving my truck.  I wish my truck had
his XLT's adjustable pedals, though.  Those are cool!

If someone wants a full-sized truck, compare full-sized trucks.  If we
compare the Tacoma to a Colorado...   Not much going on there, at
least when I did overnight test drives.

The Avalanche, well that's just an abomination.  <G>

That is interesting, my 2008 Tacoma, I4 manual, extended cab gets 25 mpg
in mixed freeway/city driving averaged over its 7500 miles.