The handling and steering feel of the 3 is very good, better than either the GTI or the WRX. It's a little stiffer than either, close to the GTI, but more raw, less damped. In terms of comfort and noise it's between the two - not as muffled as the GTI but not as rattly as the WRX.
It is a turbo, but again it's sort of between the two - you don't really feel a big kick the way you do in the WRX, but it's definitely a big delta, it sort of whooshes in. I really don't like that nonlinear power, I had another near-incident as I pulled out of a parking lot and gassed it hard, it's pulling out slowly then suddenly the turbo kicks and I start flying and have to compensate steer. Bleck. But generally the power is great, it feels fast, and once the turbo is engaged the throttle response is good. The clutch and brakes are a little vague, but not horrible. The engine feels a lot better than the WRX even though it's a bit slower because the power is much more predictable and immediate.
Cargo space in the hatch back is very good; the rear seats are too small, near useless, but they fold down completely flat which is good. It's about the same size as the WRX overall, though the WRX has better rear seats.
However there is a big problem - it's got bucket seeds with big side bolsters. If you happen to be a wide person like me, this is fucking excruciatingly uncomfortable, as the bolsters don't fit around you, but rather dig directly into your ribs and kidneys. I fucking despise this trend to put race seats in cars that don't really need them. The standard seats in all cars should be flat, eg. not race seats, and not even buckets at all. Then if you actually want race seats you can get them aftermarket, because you need to buy ones that fit you perfectly; they need to fit you like clothing, there's no one size fits all. It's fucking retarded and it kind of blows my mind. Why don't I get a choice of seats in cars? Especially in luxury cars, there should be a variety of sizes & shapes of seats.
The cabin controls in the 3 are some of the best I've seen in any car yet. They're just plain old buttons that work fine, they are intuitive and well positioned, no computer mumbo jumo or screeny shit or weird non-standard ways of doing things. (on the other hand, they have a fucking awful locking key ignition thing which is pointless and annoying).
Aside from the seats, the 3 is my favorite of these small practical cars. It's also got great reliability marks, near Honda levels (the Subaru is also pretty good and the GTI is mediocre).
BTW it's kind of stonkering how fast these cheap cars are. The 3 has supposedly done a 0-60 in 5.3 sec , the new WRX can do it in 4.8 sec ; those numbers are like super sports cars from 10 years ago.
Head to head comparison of the "hot hatches" (not really the proper hot hatches, sadly) :
Engine : Mazdaspeed 3 , no contest. The WRX is faster, but the power is so nonlinear. The 3 does have a bit of annoying turbo wimpyness in the low revs, but kicks in quick and then is nice and linear in the high revs and has plenty of punch. The GTI is a bit slow, but that's not really the problem, it's the low-passed laggy throttle that sinks it.
Cargo room : The 3 and WRX tie , both very good. The GTI is not bad for how small the car is.
Apparent build quality : GTI wins for nice feel, the 3 is a close second, WRX is cheap and plasticky, though much improved.
Actual build quality : Mazda wins, then Subaru, then GTI last; the GTI has a reputation for being very bad, but early reports claim they've finally sorted that - we'll see.
Seats : GTI by a big margin, nice design, comfortable, adjustable lumbar support. The WRX seats are okay, the 3 seats are absurdly stupid if you're not just the perfect size body for them.
Brakes : I think I give the GTI the nod on this for nice solid feel, the WRX comes in second and the 3 last with it's vague unreassuring pedal.
Quick cornering : the WRX has to win this as it's the only one you can actually toss around a corner without the wheels skittering or veering out into understeer.
Steering feel : really all three are quite good here, the 3 is maybe the most sensitive and connected to the road, the GTI feels very solid and nifty but a bit too damped.
Ride comfort : GTI by a mile, amazingly quiet and comfortable for a small car. Both the WRX and 3 are very noisey and bumpy by comparison.
Transmission : the GTI wins, the shifter is really nice, short throws; I find the clutch to be a bit too long and soft, but it's better than the 3 and way better than the WRX whose shifter is way too long and vibratey.
There's nothing seriously wrong with any of these cars, they are all excellent values and very practical and good to drive. I recommend one of them over any Audi or Infiniti or Nissan or Toyota or etc.