BBS has T2 sing the melody probably 80% of the time, even in new championship quality arrangements (modern arrangers), with short segues and changes to other parts for variety and bridges. T1 (highest) gets the most of the rest of the melody parts.

B1(the baritone part) is higher than B2, but is the hardest part to sing. It is so typically used to fill in essential parts of the chord through harmonies and dissonance that if you listen to just the B1 part, you may not even recognize what song it is (even if it is sung well!) Many of the arrangers are B1's because they are the most musically savvy and able to read and hit notes at unexpected intervals.

In the TTBB Hymn arrangements T2 is usually lead, although the T1 has nearly as many songs where it is the melody. Hope that helped...