Often the Lotus Sutra is cited as a favourite. It certainly is in the Buddhist heartlands and has been for many centuries. One of the great zen masters, Dogen, often referred to it in his writings. It contains the justly famous "Parable of the Dharma Rain":-
I bring fullness and satisfaction to the world,
like rain that spreads its moisture everywhere.
Eminent and lowly, superior and inferior,
observers of precepts, violators of precepts,
those fully endowed with proper demeanour,
those not fully endowed,
those of correct views, of erroneous views,
of keen capacity, of dull capacity -
I cause the Dharma rain to rain on all equally,
never lax or neglectful.
When all the various living beings
hear my Law,
they receive it according to their power,
dwelling in their different environments........
......The Law of the Buddhas
is constantly of a single flavour,
causing the many worlds
to attain full satisfaction everywhere;
by practicing gradually and stage by stage,
all beings can gain the fruits of the way.