Which part of the coffee brew is best?
It is not simply a matter of strong versus weak.  Rather, different qualities are extracted from the coffee over different parts of the brewing process.  The most volatile components are extracted early in the brew, and the less volatile components come out over the length of the brew.

So the distribution of flavors varies over the brew.  Total brew time is carefully calibrated in quality coffee makers to extract the most desirable flavors possible, and minimize the least desirable.

By taking some out early, you are guaranteed a bad first cup, and are consigning the remainder of the pot to be less than it could be.

For best quality, you should wait for the entire brew, so that the flavors are balanced from the entire brew time.