1.5L (114ps, 14.3kg/m) - enough
2.0L (150ps, 18.7kg/m) - good
2.3L (~260ps, ~39kg/m) turbo - very powerful
I drive a 2.3 (non-turbo, not sold in HK). Sometimes, I drive it on highway up to 160km/h, it is still very stable. Mazda3's chassis performs very well; it's firm and responsive. My friend drive the 2.0 version and they comment that the 2.0 engine react similar to the 2.3 one.