choice
I start work early by choice, because I prefer it.
He visits his parents occasionally, more out of duty than by choice.
She walks to work, not by choice but because she had to sell her car.
Although he had completed his full two years of military service, he remained in the army by choice.

SMART Vocabulary: related words and phrases

Taking and choosing
adopt
adopted
adoption
appoint
bags I...idiom
be your best betidiom
cull
faute de mieux
favoured
filterable
first choice
go for someone
picker
Robin Hood
select
selection
selective
selectively
skim
you pays your money and you takes your choice/chanceidiom