First off, there's a huge difference between a knee brace, a knee stabilizer, and a knee sleeve. You need to be clear about what you're looking for in order to get the results you want.
That being said, if you're looking for knee braces (maximum support but limited mobility) then you can't go wrong with the Shock Doctor brand. Are they a little expensive? Absolutely. But are they worth the money? I truly believe so.
If you're looking for a knee sleeve that does more prevention and increased blood flow, you'll want to look at the Viper series brand. It's performance is better than most leading brands like Nike and Under Armour, but at a much better price.
There are a wide number of knee braces and knee supports available in the market today. Different kinds of these braces and supports serve different purposes. There is no such thing as the best knee brace. You must first consult a physiotherapist or an orthopaedic doctor to have your condition assessed.Whether you are a sportsperson or not and whether you need a knee brace wrapped around your knee all through the day or not, also has a role to paly.
Knee braces today all feature different designs and are constructed out of a variety of different materials. Yes, even people in the knee brace manufacturing market all have their "favorites". But in the end knowing what type of injury you have should determine which knee brace is best suited for your situation ie patella stabilizer, double hinged knee brace, knee sleeve, Unloader knee brace, ACL knee brace, Osteoarthritis OA knee braces , Post-op knee brace etc.