Well,
one year back I had the same problem, but after spending 3 weeks in showrooms and searching the net and exploring forums I cam to the following conclusion:
Honda Civic: (For a full options car it would be)
pros.:
*a gr8 engine and a small tight body
*a nice digital speedometers and display
cons:
*expensive
*spare parts are more expensive compared to other japanese cars.
As for the mazda 3:
pros.:
*cheaper compared to the same options in a civic.
*cheaper spare parts.
cons.:
*no leather interior available (even custome made)
* Rear Bumper is a bit long making it tricky to park compared to a civic
*engine is small (only 1.6) where there are a 2.0 and a 2.3 engines in N. America and Europe.
Well As for me I got the Zoom 3, it is wonderful, as for the cons:
*Leather, can be made outside in a range of 700-1500 Dhs depending on the quality.
*Rear parking sensors can help out
*the smaller engine is better nowadays with the increasing and unstable petrol prices !!
When I got my mazda 3 the full options was like 54K something, with ABS EBD and all those stuff, Sun-roof, Xenon headlights and fog lamps, electrnic climate control . If u want a civic with the same price u would get a car with nothing, not even ABS, normal switch type AC, and normal Halogen Lamps no fog light or sun-roof of course. but for a civic with the same options as in Zoom 3 I think the price jumps to a nearly 70K Dhs as i recall.
So in the end it is up to u !! u go , u inspect . u search and u decide!!
Good Luck ma8!!
P.S. : check this out :
http://mazda3forums.com/