Most of the channels I watch look good in SD. It depends on two things: Your TV, its picture engine, how extensive the picture settings are and How good the stream is from the channel itself.
I have a sony bravia W series set. I have motionflow set to medium, sharpness off, black correcter medium, gamma at +1, Noise reduction Low, Live colour off, Adv. Contrast Enhancer low.
If you like a setting dont have it on high ever. With most TVs this produces exaggerated results and causes artefacts. motion flow helps with reducing the blurryness, The other above setting help produce better colour without loosing detail. Something like Sonys Live colour is horrible because it illuminates certain colours and it makes the image flatter by reducing detailing