Use of の vs が in 見込みのある


This example is from page 51-146 of Lake and Ura's _Learn to Read in
Japanese_.

> 見込みのある若い人を育てるのがベテラン社員の役割だ。

Google Translate gives

> Veteran employees are responsible for raising prospective young people.

This [link](http://yesjapan.com/YJ6/question/2954/item-ga-aru-vs-item-no-aru-
in-a-sub-clause) seems to say that "見込みのある" is more idiomatic than "見込みがある,"
which is what I initially thought would be the correct particle. Is there a
more general rule for using "の" vs "が" in cases like this?

