All people have different opinions, so you should probably buy some concealers and experiment with it. You may also go to sites which give out free makeup samples.
Mary Kay markets a very wonderful formula of concealer for your situation that does not flake. Another good option would be to use Maybelline brand concealer.
It is incredibly difficult to determine which concealer of the thousands on the market is the best for a face with freckles. Some good ones include The Body Shop's Ultra Smooth Liquid Concealer and Boi - ing by Benefit Cosmetics.
Avon
maybelline makes AMAZING concealers especially dream lumi touch highlight concealer. covergirl does ,too
For dark spots, you need a yellow based concealer. This will give the best overall coverage.
Concealer or powder.
concealer
try Maybeline's concealer
I have combination skin and I get blemishes in my T-zone and need to use concealer every day. The best full-coverage concealer is probably the MAC studio effects concealer, because its so thick but light and gives a really nice heavy coverage so it hides all redness and dark spots. For just a cheap, everyday concealer is the Maybelline NY dream mousse concealer, because its super light and airy and has quite excellent coverage. For under the eye concealer, the best is Bobbi Brown, but just for a cheap drugstore one, the Physicians Fomula stick concealer or The Body Shop tea tree concealer stick are both good.
I have found that Signature Club A has a great line of concealers that cover nicely without feeling heavy. My personal favorite is the mauve concealer but i also like the yellow.
Best concealer for dark circles is the Tarte Shape Tape Full Coverage Concealer, which smooths and brightens the under-eyes while simultaneously blurring the appearance of fine lines and wrinkles or also the best shade of concealer that hides the darks circles is orange family in my opinion Since dark circles are primarily blue, reach for shades in the orange family. If you have light or fair skin, use a more peachy color. If you are more in the light to medium skin tone range, look for a bisque color corrector. If you have a dark skin tone, reach for an orange-based concealer
First cover up under eye circles by using a concealer brush or your fingertips to dab concealer under your eyes. Apply the concealers under your eyes and blend the concealer in around the edges. Simply dab the concealer with the tips of your finger or brush in order to blend it. Next, apply the concealer to acne and spots. Dab your concealer onto the top of each mark, and then blend softly outwards to your skin. Use a thin layer of concealer to avoid having a caked-on look. If you have acne, avoid using your fingers to blend the concealer because using your finger can spread bacteria. Lastly, you have to set your concealer. Use a loose or compact powder foundation to set your concealer, so it does not easily wipe off.