Choose, select, elect, opt, pick, cull, prefer, single are comparable when they mean to fix upon one of a number of things as the one to be taken, accepted, or adopted or to make such a determination.
Choose commonly implies both an act of judgment and the actual taking or adoption of what is fixed upon.
Select usually implies a wide range of choice and discrimination or discernment of values in making one’s choice.
Elect often implies a deliberate choice, especially between alternatives, or a careful selection of some out of many possibilities; ordinarily, it carries a stronger implication of the rejection of that not chosen than either of the preceding words.
Opt (often with for) implies an election between alternatives, often specifically, in the case of inhabitants of territory transferred by treaty, between retaining one’s former citizenship or acquiring citizenship in the new state.
Pick implies a careful selection, often on personal grounds; cull, a nice or fastidious choice.
Prefer implies choice that indicates what one favors or desires; it does not, however, always carry an implication of taking or adopting what one chooses or of getting one’s choice.
Single (usually with out) implies choice or election usually of an individual person or thing from a number.