decide on

decide on (someone or something)

To choose someone or something, usually after a period of deliberation. Yes, Holly was a strong candidate, but we ultimately decided on someone else for the job opening. After agonizing over the menu, I finally decided on mint chocolate chip ice cream.
See also: decide, on
Farlex Dictionary of Idioms.

decide (up)on someone or something

to choose someone or something; to make a judgment about some aspect of someone or something. (Upon is formal and less commonly used than on.) Will you please hurry up and decide upon someone to vote for? I decided on chocolate.
See also: decide, on
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

decide on

or decide upon
v.
To choose something or someone after deliberation: We decided on green as the color for the nursery. I've decided upon the red shoes; you can put the black ones back.
See also: decide, on
The American Heritage® Dictionary of Phrasal Verbs.
See also:
  • accompany (one) on a/(one's) journey
  • accompany on a journey
  • brief (someone) about (someone or something)
  • brief about
  • be out of (one's) league
  • be out of somebody's league
  • be/have done with somebody/something
  • bargain
  • bargain for (someone or something) with (someone)
  • a dog in the manger