That is known as a ristretto (literally restricted shot). Usually these are higher bodied sweeter shots. As a general rule the last part of the coffee is higher in acids with less body (just remember when it comes to coffee and what is best for it most rules can be bent or at least warped).
What you should do is get three or more shot glasses and pull the first third into the first glass, the second third into the second glass and the third third into the last glass. This will give you an idea as to what each part of an espresso pull tastes like and you can make up your mind from there.