Well this is certainly an old post, but the topic is correct so I'm going to revive it. Now that the fuel economy numbers are out, the CX-3 isn't looking like as much as a slam-dunk as it was before. The main details it has going for it now are the sportiness of its ride next to the competition and it seems better equipped than many of its competitors. However, the amount of room you get is behind most of its competitors.
On the flip side, both the Mazda 3 and the CX-5 get more cargo and people room. In terms of the CX-5, you get more than double the space with the seats up, better ground clearance and optional all-wheel-drive (important for me because of snow), and only slightly worse fuel economy. What's more, the CX-5 has been available for a few years so it's possible to get a used model for less. Taking those things into consideration, I'm starting to lean much more towards to CX-5 as long as it isn't too big and still handles well.
Ideally, I'm wanting a compact vehicle that handles like a tall hatchback like the Vibe I currently own. It has a higher seating position that most hatchbacks, but still handles like an agile small car. This is what a crossover means to me, not just a smaller SUV with awkward handling like the Trax. The CX-3 looks to fit that quite well, but at the sacrifice of space. The CX-5 could potentially work as long as it isn't too big for my tastes. The Mazda 3 would cut the difference, but I really want the AWD after the last few years of heavy snowfalls. Winter tires can only do so much if you can't get moving in the first place.