expression
no difference; indistinguishable; same thing
Used to say that two or more things are essentially the same, with no meaningful difference to choose between them. Often appears in the pattern 〜も〜も選ぶところがない or 〜と〜は選ぶところがない.
この二つの案は選ぶところがない。
There's nothing to choose between these two proposals.
あの二人の実力は選ぶところがないほど似ている。
Their abilities are so similar that they're practically indistinguishable.
Both express that there is little difference, but 選ぶところがない is a more direct statement about indistinguishability, while どんぐりの背比べ is a set phrase meaning 'they're all much the same' (often with a slightly negative nuance).
Literally 'there is no place to choose', from 選ぶ (to choose) + ところ (place/point) + がない (there is no). The expression is idiomatic and its origin is transparent.