The homebrewer has two types of yeast to choose from;
liquid yeasts or
dry yeasts. For some this argument is similar to a "taste-great less filling" debate or "Ford versus Chevy" discussion and is just a matter of preference while others are very passionate about their preference. Good beer can be made from both dry and liquid yeast and both have their advantages and disadvantages. While many homebrew enthusiast claim that dry yeasts are a poor fermenter and can produce undesired flavors since they are not as pure a culture as a liquid yeast others favor the convenience and lower cost that dry yeast offers.
Dry yeast is inexpensive, convenient, hardy and does not require a starter. However most experts agree that a starter would be beneficial when using a dry yeast. A simple starter to rehydrate your dry yeast is available right in your brew kettle. A starter will create a larger number of yeast cells that are added to the wort resulting in a more efficient the fermentation process. A more efficient fermentation results in a better quality beer with less likeliness of contamination. To create a starter simply remove 1 cup of wort 30 minutes before the end of the boil and allow to cool in a covered container. Add the dry yeast and allow 10-30 minutes to proof. After this time the yeast should be visibly churning and/or foaming, and is ready to pitch. I also find the addition of a good yeast nutrient to your wort to be very beneficial. The best nutrient is actually dead yeast cells in the form of Vegemite or Marmite yeast extracts. The addition of a yeast nutrient to wort promotes a healthy and hearty fermentation resulting in a beer with a lower final gravity. You can use the trub from your kettle as an excellent yeast nutrient.
Dry yeast also stores easily and it is hardy. Dry yeast tends to produce a more solid yeast cake making racking easier and producing a clearer final product. Also, dry yeast is much cheaper than liquid yeast. Liquid yeast can run 25% of the total cost to brew. Fermentation with dry yeast starts quickly and helps prevent your beer from getting an infection due to lag time. Since dry yeast can be stock-piled you won't find yourself running out to your local brew shop to pick some up if you accidentally forgot to purchase it.
However, the selection of good dry yeasts is quite small, and therefore limits the range of possible beer flavor profiles you can get with the yeast. Liquid yeasts are pure cultures or blends of pure cultures and come in a extremely wide range of choices allowing a lot of possibilities when it comes to affecting the flavor profile of your beer (and if you want to make a lager, liquid yeast is your only option). There are a many wet yeast strains available. Each produce a distinct tasting beer. There are only a few dry strains available. Simply put, all of the subtle flavors offered by wet strains are simply not available in dry form. Some of the most popular ones are, but certainly not all. With liquid yeast you can propagate, split, and reuse wet to get your costs down, if you are careful about sanitation and want to take the time to do so. You can split, and re-split to get the cost on a per batch basis to less than half that of dry yeast. But, this takes a lot of time and effort.
For the absolute best beer, there is no question that liquid yeast is a superior product and worth every bit of the extra cost. But like so many things, we have time, money, and quality from which in many cases we can only choose two. If you want high quality and want to save time, buy a liquid smack pack with a higher price tag. If you want high quality and want to save money, propagate from a liquid smack pack which takes a lot of time. If you want to save time and money, buy dry but recognize the fact that you probably won't get all the subtle flavor choices you desire and possibly a lower quality, but nevertheless a good, beer.
