I personally like the main cabin better, for three reasons:
(1) The small cabin is almost always filled to the last seat, while in the back of the bus there is often empty seats left
(2) If children are present in rows 3 and 4, it can get very loud in that small space
(3) If you are seated in the small cabin, you have a direct view of the first class cabin. Too painful.

Row 12 is one of my favorite rows: Far enough away both from the baby row 10 and the beginning of economy class after row 14.