Not sure what connections you have on the home cinema system and I'm not sure whether you have a separates system or an all in one system but basically you need to connect the laptop to the home cinema system with the output from it going to the TV.
HDMI from the laptop to the home cinema system then HDMI from it to the TV will give the best quality if you can connect it that way.
In fact in general all sources should be connected to the A/V Receiver with one HDMI going to the TV.
It depends on what connections you have available as to whether or not you can do that though.
With regard to streaming via the PS3 the quality should be the same unless there's some sort of dynamic rescaling taking place.
Some devices are more capable at upscaling than others and depending on which device is doing the upscaling you may notice a difference in quality.