my 2 cents
I have driven both the mazda 3 sp23 hatch and just this morning the civic sport in auto form the civic is much better in quality finish (feels generally more soild) performance and handling the only advantages the sp23 would have over the Civic is extra 300cc engine capacity and maybe the Bose option stereo which is overated.
The civic's betters the 3 by having 5 speed tipo auto box oppose to the 3's 4 speed box has standard leather and sunroof and a much better interior overall plus you gotta love those CTR rims michellin tyres package and lastly its a HONDA.