Let me put the "other side of the case" forward. Not because I
have decided one way or the other, but because I am interested in
yours (and others) response:
*Looks: Like comparing chalk and cheese. The Civic has an elegant,
refined look. The Mazda 3 (especially with the spoiler, etc) has a
sporty, sexy look.
*Civic is a newer model: true, can't dispute this. This might
impact on resale value in the future. In 3 years, a 2007 Civic will
still be "current model" or similar, whereas the Mazda 3 will be a
"has been".
*Interior: matter of taste, some like the Civic's interior, some
don't.
Let me make some other points:
*Subjective driving : many people say that the Mazda is much more
of a driver's car than the Civic. I have test driven them both
(though the Mazda I test drove was a 2.3, not the 2.0 one) and can
confirm that handling, brakes, steering are better on the Mazda.
It's much more fun to drive.
*In Australia, the Mazda 3 is Japanese made and the Civic is
Thailand made. This may or may not impact on build quality.