They are pretty much polar opposites on the beer spectrum. In terms of taste, Bud Light tends to be, to put it nicely, "crisp," which is to mean essentially tasteless, save for some mild corn malt flavor. Guinness has a deeply-malted, chocolate-roasted barley taste and characteristically creamy head. read more
In terms of color, Bud Light is, well, light, and Guinness is dark. The SRM scale, on which most beers score between 2 and 40, Bud Light scores between 2 and 3, whereas Guinness scores between 36 and 38. read more