Terence,
Phormio 454 (tr. John Sargeaunt):
So many men so many minds, every one has his point of view.
quot homines tot sententiae: suos quoique mos.
Horace,
Satires 2.1.27-28 (tr. H. Rushton Fairclough):
For every thousand living souls, there are
as many thousand tastes.
quot capitum vivunt, totidem studiorum / milia.
Hotace,
Epistles 2.2.58 (tr. H. Rushton Fairclough):
After all, men have not all the same tastes and likes.
denique non omnes eadem mirantur amantque.
Ovid,
Art of Love 1.759 (my translation):
There are as many characters in human hearts as there are shapes in the world.
pectoribus mores tot sunt, quot in orbe figurae.
orbe codd.: ore Bentley
Persius 5.52-53 (tr. Susanna Morton Braund):
There are a thousand types of humankind, and their experience of life is variegated—they each have their own desires and no single prayer fits every life.
mille hominum species et rerum discolor usus;
velle suum cuique est nec voto vivitur uno.
On the Greek side, see Philemon, fragment 93 Kassel and Austin, lines 10-11 (tr. F.A. Paley):
But in the human race one always finds
As many bodies, just so many minds.
ἡμῶν δ' ὅσα καὶ τὰ σώματ' ἐστὶ τὸν ἀριθμὸν
καθ' ἑνός, τοσούτους ἔστι καὶ τρόπους ἰδεῖν.
11 καθ' ἑνός codd.: καθ' ἕνα Meineke
Herbert Richards, "Further Emendations of the Greek Comic Fragments,"
Classical Review 13 (1899) 426-428 (at 428):
Καθ' ἑνός is nonsense and Meineke suggested 'nonne καθ' ἕνα scribendum?' no doubt meaning it to go with what follows. The point is that, whereas all the animals of a species are alike, in the human race there are as many characters as individuals. Quot homines, tot ingenia. You find, taking men one by one (καθ' ἕνα) that each is different. Cf. the καθ' ἕνα in Philemon's remark on the nuisance of friendly questions as to how you are (M. 4, 15: Κ. 2, 490 [= fragment 47 Kassel and Austin]):
πολὺ μεῖζον ἐστὶ τοῦ κακῶς ἔχειν κακὸν
τὸ καθ ἕνα πᾶσι τοῖς ἐπισκοπουμένοις
δεῖν τὸν κακῶς ἔχοντα πῶς ἔχει λέγειν.