Honestly the Impreza's got the best visibility of any hatch out there right now. Which Mazda3 did you find had bad visibility, the 2013 or the new 2014? I'm finding the 2014 is fine except out the back, but that's what back-up cameras are for, and the blind spot monitoring works great also (on i Touring trims and above). The A-pillers are a little thick, but they're also more vertical than a lot of cars these days, which helps reduce the obstruction they cause. The 2013 was pretty bad visbility-wise, but most cars are going downhill in this area due to evolving safety requirements. The first-generation Mazda3 was even worse, trust me.
The Elantra GT's A-pillars are on the thick side, but the visibility is still decent. But it gets a 2.0L DI engine early next year, and I'd wait for that, the 1.8L it has now is pretty gutless.
Kia's supposedly got a 2014 Forte hatch coming, but it was supposed to be here by now and so far is completely MIA, no word from Kia on the delay. Too bad, it was supposed to get a 1.6L turbo and 200 HP. It might show up in Q1 2014.
There isn't much else out there for hatches. Don't go near Scion, they're all outdated.
There's always the VW Golf, checked that out yet? Assuming you can deal with the legendary (or mythical depending on who you ask) VW reliability.
Speaking of reliability, how about the Fiat 500? Hahaha, just kidding.
Thick pillars are just a fact of life these days though, blame crash testing and all that. No one makes go-carts with collapsing roofs anymore. C pillars are thicker wherever you go and B pillars are reasonably hefty too. D-pillars are actually disappearing as manufacturers shrink and then eliminate the rear-quarter window, or integrate it into the rear door as Mazda and Kia have done. A pillars vary, as I mentioned Subaru got them down pretty slim, Hyundai's are thick, and some manufacturers are in the middle but use various methods to reduce the visual cross-section at least. On the upside, these days you can get most compact cars with a selection of aids to compensate, including back-up cameras, blind spot monitoring systems, rear radar sensors for parking, etc.