2011 Sonata is built on the same platform as the 2011 Optima. 2011 Sonata is available in 9 trims: ranging from the GLS Manual to the Hybrid version of the car. The success is greater than on 2011 Kia Optima and that's because of the main principle - Hyundai Sonata is more popular car in the world auto industry. But to say truth consumers even do not know exactly that the winner in base trims from 2011 Hyundai Sonata vs. 2011 Kia Optima is both of these cars, because they are same in everything, except exterior. Exterior and interior are really alike of Optima and Sonata.
The base trim of 2011 model is called GLS Manual and it offers consumers exact engine what is in Kia Optima - 2.4L, 4 cylinders and 198 HP and its average price is $18,500
Next trim of 2011 Sonata is GLS Auto and it offers us the same engine with automatic transmission.
But 2011 Hyundai Sonata GLS Auto PZEV offers us
* 2.4L I4, 16 valves, 190 hp
* 6 speed automatic transmission
* 22 mpg (city) / 35 mpg (hwy)
The price range between 2011 Hyundai Sonata 9 Trims is: $18,500 - $27,000
The last Trim of Hyundai Sonata after Hybrid Version is called- Sonata Limited Auto TGDI
* 2.0L I4, 16 valves, 274 hp
* 6 speed automatic transmission + improved fuel economy pack
* 22 mpg city / 33 mpg hwy
The decision is up to you, if you just like both of these cars, you should choose the model what looks prettier for you, because the price range between them is almost same, performance & engine is same and almost all other features too. The popularity of the car is high in both of them, but for my personal view 2011 Kia Optima looks better for me.