There are two general style classifications for pipes: straight & bent.  A straight pipe has a straight shank and stem and will be more inclined to directly transmit heat and moisture to the palate.  A bent pipe has a curved shank and stem and tends to collect more moisture at the bottom of the bowl, below the bend of the shank.  Both styles have a distinct feel and balance in the hand and mouth, which pipe smokers appreciate for different occasions or moods.