Mishnah Berurah — משנה ברורה

Without concentration - But if the one saying a lot is also [able to say it] with concentration, then [certainly] it is better to say more. And if the one saying a little has an extenuating circumstance and he is not able to say more, or if he estimates himself that if he says more, he will not be able to concentrate, and so he lessens his supplications but says them with concentration - he is considered before Hashem to be like one someone who has plenty of time and is able to lengthen his supplications with concentration. And regarding this we learned: "One who brings a substantial [sacrifice] and one who brings a meager [sacrifice have equal merit], as long as he directs his heart towards Heaven". The same thing applies to learning Torah, because everything is dependent before Hashem on whether one does everything in his power to do. A person who is a master in Torah and is able to understand and learn, he may hold back from saying a lot of supplications and requests which are printed in the prayer books, and it would be better for him to learn Torah instead. A person must establish for himself a time to learn Mussar (Jewish literature that provides virtue-based instruction for moral and spiritual character development) every day, whether a little or a lot, for "a person who is greater than his fellow, his evil inclination is greater than his [as well]". And the antidote for the evil inclination is the words of rebuke of our sages.