I love Ki, but Schneiderlin is better without a shadow of doubt.
I watched Ki a lot ever since he was at Seoul with Lee CY and there is no question about his quality. He is a good player for most team, would even be first choice for Spurs, Liverpool and Southampton to give some perspective. But for a side like us who wants to make the next step up to challenge for the title, he will only be a good squad player and nothing more. After the debacle with Park, I am not sure any Koreans would want to come here to sit on the bench.
His biggest strengths would be passing, dealing with pressure and intelligent positioning. Shots and set piece abilities are good too.
Cons of his game is weak defensively, especially in 50-50 challenges and aerially. He is what Anzac would describe, a perfect DLP, like a young Arteta.