You should always choose the lesser of two evils.

[De duobus malis semper minus tamen est eligendum.]

Thomas à Kempis (c. 1380-1471) German-Dutch priest, author

The Imitation of Christ [De Imitatione Christi], Book 3, ch. 12, v. 2 (3.12.2) (c. 1418-27) [tr. Knox-Oakley (1959)]
    (Source)

In this context, Thomas is speaking of the evil (suffering) of resisting temptation and losing out on fun times in this world, compared to the evil of eternal damnation, e.g.,

If thou say, that thou art not able to suffer much, how then wilt thou endure the fire hereafter? Of two evils the less is always to be chosen. That thou mayest therefore avoid the everlasting punishment, endeavour to endure present evils patiently for God's sake. [Anon. (1901)]

See also Cicero.

(Source (Latin)). Alternate translations:

Of two evils, the less evil is to be taken.
[tr. Whitford/Raynal (1530/1871)]

Of two evils, the lesser is to be chosen.
[tr. Whitford/Gardiner (1530/1955)]

Of two evils the lesse is alwaies to be chosen.
[tr. Page (1639), 3.12.5]

Nature, as well as Religion, teaches Men, of Two Evils to choose the less.
[tr. Stanhope (1696; 1706 ed.), 3.13]

Of two evils, the least is to be chosen.
[tr. Payne (1803), 3.9.4]

Of two evils the less is alway to be chosen.
[ed. Parker (1841)]

Of two evils, the least is to be chosen.
[tr. Dibdin (1851), 3.10.1]

Of two evils we ought always to choose the less.
[ed. Bagster (1860)]

Of two evils we should always choose the less.
[tr. Benham (1874)]

Of two evils the less is always to be chosen.
[tr. Anon. (1901)]

Of two evils, the lesser is always to be chosen.
[tr. Croft/Bolton (1940)]

Of two evils always choose the less.
[tr. Daplyn (1952)]

Of two evils, always choose the lesser.
[tr. Sherley-Price (1952)]

One must always choose the lesser of two evils.
[tr. Knott (1962)]

You must always choose the lesser of two evils.
[tr. Rooney (1979)]

Always choose the lesser of two evils.
[tr. Creasy (1989)]