But atheism and science are integral to liberalism. The unreasonableness and rank illiberalism of mythology and pseudo-science are anathema to a healthy lifestyle and civilized society. The attitudes, beliefs, and practices of Aristotle and Rand were sometimes highly irrational. So even the finest of proto-liberal thinkers are far from being true or pure liberals.
Still, we have to work with what we've got, so here is the best so far:
Romans
1. Cicero
2. Lucretius
3. Aurelius
4. Virgil
5. Horace
6. Seneca
7. Juvenal
8. Terence
9. Publius
10. Ulian
Europeans
1. John Locke
2. Voltaire
3. Adam Smith
4. Denis Diderot
5. Francis Bacon
6. d'Alembert
7. Montesquieu
8. Helvetius
9. d'Holbach
10. Pierre Bayle
Americans
1. Thomas Jefferson
2. Benjamin Franklin
3. John Adams
4. Thomas Paine
5. James Madison
6. John Jay
7. Albert J. Nock
8. John Quincy Adams
9. Gouveneur Morris
10. John Marshall
Austrians/Libertarians
1. Ludwig von Mises
2. Frederic Hayek
3. Henry Hazlitt
4. Murray Rothbard
5. Robert Nozick
6. Frederich Bastiat
7. Lysander Spooner
8. Jacob Hornberger*
9. Robert Poole*
10. James Bovard*
Objectivists
1. Ayn Rand
2. David Kelley*
3. Stephen Hicks*
4. Leonard Peikoff*
5. Chris Sciabarra*
6. Nathaniel Branden
7. Robert Bidinotto*
8. Robert Tracinski*
9. John Lewis
10. Yaron Brook*
*magnificently still living