The life according to reason is the happiest

If reason is divine, then, in comparison with man, the life according to it is divine in comparison with human life. But we must not follow those who advice us, being men, to think of human things, and, being mortal, of mortal things, but must, so far as we can, make ourselves immortal, and strain every nerve to live in accordance with the best thing in us; for even if it be small in bulk, much more does it in power and worth surpass everything. And this would seem actually to be each man, since it is the authoritative and better part of him. It would be strange, then, if he were to choose not the life of himself but that of something else. And what we said before will apply now: that which is proper to each thing is by nature best and most pleasant for each thing; for man, therefore, the life according to reason is best and pleasantest, since reason more than anything else is man. This life therefore is also the happiest.

Aristotle, The Nicomachean Ethics (Oxford University Press, 2009) pp. 195-196