That's really the thing that'll make up your mind between them. Personally, I'd opt for the inner child and revel in the outrageous execution of the Kia Optima every time.
The brand's signature "tiger nose" grille shape, a creation of design boss (and ex-Audi man) Peter Schreyer, is echoed everywhere from the top of the windscreen glass to the grey plastic that frames the dash and centre console.
That distinctive side-vent is a visual swipe at BMW's M-cars. The alloys are "only" 18-inchers, but look more like 20-inch rims thanks to an ingenious spoke-shape that directs your eye right out to the corner of the sidewall.
That's a lot of presence for a $46,990 mid-size sedan and you also get a lot of kit. There's only one Optima trim level for New Zealand and it includes everything from leather upholstery to a clever reversing camera that materialises out of the rear-vision mirror. Even a dashboard graphic to remind you to straighten the front wheels before you charge off backwards.
Will it surprise you to learn that the Optima's performance isn't as striking as its looks? It couldn't be really, although there's nothing dramatically wrong with the car's 148kW/250Nm 2.4-litre four-cylinder engine and six-speed automatic gearbox.
There are differences in suspension tune between the Kia and its Hyundai sibling. The Optima gets the so-called "ANZAC" package specific to this part of the world, while the i45 has recently benefited from suspension changes out of Korea. Which has the edge? Impossible to say without running the cars back-to-back and really not important, as neither is especially broad in its talents.
The Kia's dynamics are decent enough for undemanding drivers, but the steering suffers from rack-rattle in bumpy corners, the ride is unsolved and the road noise significant. It grips well and can corner fast, but if you want a mid-sizer with a truly sophisticated chassis, buy a Ford Mondeo or Peugeot 508.
If you'd rather your family sedan looked like a Hot Wheels car and be loaded with kit, Kia might have the car for you. For all its obvious faults, I really rather like the Optima because it doesn't seem to take itself too seriously.
The bottom line:
Kia has gone wild with the styling of the Optima and it works. It's a Hot Wheels car for the family ... even if it's not especially hot.