First, it's important to understand the terms.
Consistency: Foundation comes in 3 main forms - cream/stick, powder, and liquid. Creams tend to be a little bit thicker and generally come in a stick or compact, allowing for more buildable coverage. If you are only using foundation on certain areas of your face, creams are good, though some formulas may be too heavy for oily skin. Powder foundations can come in a loose or pressed form. Although they are often associated with subtle coverage and mattefying properties, there are definitely some powder foundations that are great for dry skin and offer heavier coverage. Liquid foundations are lotion-like and come in a large variety of different looks and types.
Coverage: When you're shopping for foundation, check the packaging or ask a sales associate about the level of coverage that a foundation will offer you. Full coverage products are heavier foundations that conceal the most, while sheer coverage adds only a little bit of color, and medium coverage is somewhere in between. For those of you, who need foundation to conceal a lot of redness, blemishes, or sunspots, look for a full or medium coverage level. If you are using foundation to simply even out your complexion, try a product with sheer coverage.
Skin Type: Some foundations contain oil, while others are oil-free. If you have oily, combination, or blemish-prone skin, you should
definitely opt for an oil-free foundation. Non oil-free foundations are ideal for mature or drier skin types. The majority of people have combination skin, so brands usually like to advertise the fact that a foundation is free of oil. Thus, unless a foundation says oil-free or water-based, you can assume that it does contain some type of oil.
Finish: Foundations have 1 of 3 finishes. A matte finish will leave you will a powdered, shine-free, porcelain look like Kate Middleton
or Taylor Swift. Alternatively, a dewy finish will give you a luminous and shimmer-like glow. For example, celebrities like Jennifer Lopez or Hayden Panettierre often wear foundation with a dewy finish. If you want to achieve a dewy finish, a liquid foundation will be your best bet. Lastly, a satin finish is somewhere in between and perhaps the most natural-looking, offering a slight and subtle glow. Jennifer Aniston rocks this look a lot. Check out Mila Kunis with her satin finish on the red carpet.
...keeping this in mind - I've created a little diagram with some product suggestions for different combinations of these factors to help you find a great product for your individual needs. Websites like Temptalia also make some great tools for finding foundation. The only difference with this one is that all of the products that I have listed are paraben and phthalate-free. Yay! I haven't tried all of them, so I can't attest to their level of effectiveness (how long-lasting it is, if it's easy to apply, etc.). But I have tried many great foundations, which I tried to include in this post.
For those of you, who like sheer coverage, you can always try an airbrush foundation. Maybelline Dream Nude Airfoam ($9.99) is a great drugstore buy, or try Sephora Perfection Mist Airbrush Foundation ($26). These products have air incorporated into them so that they feel super light-weight.
Since everyone's skin is different, the efficacy level of each foundation will vary with each person. Hopefully, now you a starting place when it comes to finding a great foundation and a better idea of what to look out for!