The difference between Single Malt and Blended Malt Scotch are numerous. The initial difference is the meanings of "Single" and "Blended". These terms refer to the difference in how many distilleries created the distillate. Single means that one distillery created the distillate whereas blended means that multiple distilleries did.
In terms of flavor, Single Malts and Blended Malts will have differences. These differences will stem from the distillate made from different stills, barley from different regions, and the way they are blended as well. Blended Malts can also have different distillates mixed in after as well which will create more change in the flavor
The large majority of consumed Scotch are Blended Malts, however, Single Malts are still extremely popular. The important thing is to remember that one is not better than the other. The better of the two is entirely up to personal preference.