Well, if you're talking about streaming, you are probably going to be doing it from the network's website, so Safari, Firefox or Chrome would be good. Chrome may be the best of these since it has it's own built-in version of Flash player. Some stations/networks may have some variety of viewer or helper app that you would get from their site, but most seem to be moving away from this.
If you want to capture Over the Air TV, or even Cable TV feeds, Elgato's EyeTV is excellent. You need some hardware to get the signal to the software though.