Which sentence in each pair sounds more formal?

1. 
   A: Ricky promised to love her always.
   B: Ricky pledged to love her always.
2. 
   A: Tom swore he would take revenge.
   B: Tom vowed he would take revenge.
3. 
   A: Lou wagered a lot of money on the result of the elections.
   B: Lou bet a lot of money on the result of the elections.
4. 
   A: Lina made a resolution at New Year to give up smoking.
   B: Lina made a vow at New Year to give up smoking.