Choosing the best vermouth is largely a matter of personal taste, though there are some factors to consider when making your selection. The two main categories of vermouth are sweet and dry, though there are also products that fall in the middle of that range. Sweet vermouths have a higher sugar content, while dry varieties contain a higher percentage of alcohol, so you can base your choice on which of those characteristics you are looking for. If you are looking for a good white wine substitute to use in your cooking, then you might want to look at dry vermouths. Cocktail recipes can call for either type, and you can also drink high quality vermouths straight or on the rocks.
Vermouth is a type of alcohol that is typically referred to as wine that has been fortified and aromatized. Most vermouths are made from a white wine base, though others use a mixture of grape juice and alcohol known as mistelle. Aromatic herbs and spices, and additional alcohol, are then added to create the final product. The addition of grape brandy is one way these wines are fortified, though other distilled alcohols are sometimes used instead. Due to the different bases and additives used in making vermouths, each one has its own unique taste.
There are two main ways to select a good vermouth, one of which is whether it is sweet or dry. If you are looking for vermouths to use in cooking, then you will typically want to find a dry variety. Dry vermouths can be used as white wine substitutes in cooking, usually with good results. These vermouths are often well suited to use in sauces, especially for fish, though they can also be useful as a component in marinades. The sweet variety is typically better suited to cocktails than cooking, though even some cocktail recipes call for dry vermouth.
If you are looking for a vermouth to drink as an apertif, or use in cocktails, you should choose one that will appeal to you. Part of that selection process will be whether you want a dry product with more alcohol content, or a sweet one with more sugar. There are other factors at play as well though, since vermouths are made with such a wide range of spices and flavorings. Some products are peppery tasting, while others have hints of cinnamon or cloves. You may need to buy a few bottles and experiment to find the vermouth that you find the most appealing.