I think RealTek still cannot process the Blu-ray menu of BD-ISO. Therefore I don't know how to view the extra features using BD-ISO using RealTek. As a whole Sigma chip is generally better but unfortunately the 8643 cannot handle 3D and realvideo.
I have borrowed a media player from friend using Realtek and I have to agree with what most people mentioned. Picture quality of Sigma chip player is better, but Realtek is more responsive and is good enough for say 46".