It depends on your method. Generally, it is more cost effective to buy whole flower and make your own infusions, but a lot of people enjoy the convenience of concentrates. It really is a personal preference. I go into greater detail in Cannabis 101, including the difference between indica and sativa.
Budtenders are also very helpful, so don’t be afraid to speak up when you visit the dispensary. Just ask yourself what you want out of the experience. Do you want to be giggly? Do you want to relax? Is it medicinal? What activities do you plan on doing? Are you looking for creativity? Knowing the answer to these questions will help you and your budtender choose the right strain for you.