From my experiences of taking OC almost every trip, mostly
307.
Let me rank them according to the number of times it is being
played: 
1. "Doors, are closing, ti ti ti ti ti ti" (The
most)
2. "Thank you for travelling with SMRT Buses."
3. "Please hold on to the grabpoles or handgrips when standing
in the bus."
4. "Welcome aboard SMRT Buses"
5. "Please move to the rear for the benefit of boarding
passengers."
6. "Please do not leave your belongings behind."
7. "Attention please, this bus is affected by service diversion
ahead, please check with our service leader for details."
(The least)
I think somemore...maybe....SMRT Will Wish Everyone a Happy
Chinese New Year/Merry Christmas/Hari Raya etc.
