When it comes to fermentation, they are both yeast, and will both consume sugars, however, dry yeasts aren't available in as many different strains as liquid cultures. You definitely cannot make a true Witbier, or Hefeweizen without the proper yeast. Someone correct me if I'm wrong, but I don't think you can get those yeasts in a dry variety. There are many more choices with liquids, but liquids do require starters, and are more expensive.
There are many here that will argue about liquid vs dry, but I am from the philosophy of "what type of yeast do the breweries I like use?"
Anyhow, there are some great clean fermenting dry yeasts, but again, for certain styles liquid cultures are a must. Price will be one of the largest factors.