All you experts out there...what is the best finish type and brand for a Brazialian teak (cumaru) floor? I will soon have one installed, and I want to pick the finish that scratches the least, cleans the most easily, and protects the wood the best.

Cumaru is a very hard exotic wood. There are a couple of ways to go when finishing these floors. One is using a tung oil type floor finish. This will penetrate the wood more so than surface coatings and should not pose an adhesion problem. They are easy to touch up for the homeowner. A couple of brands would be "Waterlox" and "Watco". The other way to go would be with a urethane floor finish. ALL floor finishes will scratch and you'll need to test them on pieces of flooring to determine compatability and good adhesion. My personal choice would be to apply one coat of Park's Universal sealer and two to three coats of a high quality waterborne urethane. Examples are; Bona Traffic, Basic's Street Shoe, Trex+. Acid cured and moisture cured urethanes are also very tough. However, they are extremely flamable and may have adhesion problems with an oily exotic. Plus, they smell very bad and are a health concern till cured. I don't use them anymore. OMU's aren't quite as durable but are inexpensive and easy to apply. Many pros prefer them.

gary has it just right for ya my only tip would be to make sure you sand and finish it the same day.
DO NOT SAND THAN COME IN THE NEXT DAY TO FINISH.
have heard of lots of adhesion problems when the oil rushes to the top during the night and the waterborne poly will not stick to the oil.
i am a little new to finishing and have just learned about tung oil and just finished some solid stairs i did with cumaru with tung oil and i have a new friend. why anyone would want poly on their brazilian exotics is beyond me, tung oil is the way to go.

With wood that hard I'd use a penetrating finish (Tung oil is good, as are others).