One difference I noticed when driving the 3 (I drove a 4-door) and the Si almost back-to-back is that you sit a lot closer to the front axle in the Mazda. It kind of gives the sensation that it's going to roll over its front tires a bit more in cornering, and this is just driving a bit aggressively around town. The Si puts you further back from the front wheels and has suspension settings that do a better job of controlling body roll. Plus the pedals, shifter and steering of the Si are the typical perfect Honda stuff while the 3 isn't quite as nice. Interior finish is a bit nicer in the Si as well. Like, the material the dash is made out of and the leather on the steering wheel are a bit nicer. The Si has better seats and better visibility. The design of the 3's interior is nice but some of the materials look a bit cheap compared to the Si. Since the price and performance are nearly identical it mainly comes down to whether you want the ugly car with less features that drives better, or if you want the nice lookin car with more features that still drives alright but not quite as nicely.