In U.S. publishing, the contents page is generally referred to internally (that is, within the publishing house) as the "Table of Contents" or "TOC"; but the reason for that designation, I think, is to maintain maximum clarity in markup, etc., given that the body copy is generally referred to as "content" (if not "body copy").
Nevertheless, the overwhelmingly more common heading to use for the table of contents in the published book or periodical is simply "Contents"—if any heading is given at all. Books do tend to include that heading, in my experience, whereas periodicals often leave it to the reader to recognize the TOC for what it is. The designation "Table of Contents" seems a bit old-fashioned to me.
UPDATE (April 4, 2017)
By way of testing my impressions in a reasonably objective way, I ran a Google Books search for "table of contents" and then checked the first 25 matches to see how each book had handled its contents page. The results were surprisingly one-sided, given that the match in the first place was for the phrase "table of contents." Here is how the matches came out:
Contents page is headed 'Contents':
Drew Hyland, Plato and the Question of Beauty (Indiana University Press, 2008)
Stephen King, On Writing: A Memoir Of The Craft (Simon & Schuster, 2000)
Charles Mann, 1491: New Revelations Of The Americas Before Columbus (Alfred A. Knopf, 2005)
Ron Chernow, Alexander Hamilton (Penguin, 2004)
Stephen King, The Stand (Anchor Books, 2008)
Henry Cloud & John Townsend, Boundaries: When to Say Yes, When to Say No—To Take Control of Your Life (Running Press, 2004)
Emile Durkheim, On Suicide (Penguin, 1897/2006)
Rachel Carson, Silent Spring (Houghton Mifflin, 1962/2002)
Edward Said, Orientalism: Western Conceptions of the Orient (Penguin, 1978/2006)
C. Wright Mills, The Sociological Imagination (Oxford University Press, 1959/2000)
James Stewart, Calculus (Brooks/Cole,2008)
David McCullough, Truman (Simon & Schuster, 1992/2003)
Louis Sachar, Holes (Farrar, Straus & Giroux, 1998/2008)
Anthony Bourdain, Kitchen Confidential: Adventures in the Culinary Underbelly (Bloomsbury, 2000)
Charles Guignon & Derk Pereboom, Existentialism: Basic Writings (Hackett, 2001)
Anthony Robbins, Awaken the Giant Within: How to Take Immediate Control of Your Emotional, Physical and Financial Destiny (Free Press, 2007)
Simon Wiesenthal, The Sunflower: On the Possibilities and Limits of Forgiveness (Alfred A. Knopf, 1976/2008)
Kevin Leman, Sheet Music: Uncovering the Secrets of Sexual Intimacy in Marriage (Tyndale House, 2002)
Cynthia Kaufman, Ideas for Action: Relevant Theory for Radical Change (South End Press, 2003)
Mitchell Duneier, Sidewalk (Farrar, Straus & Giroux, 1999/2001)
Bruce Jarrell & R. Anthony Carabasi, NMS Surgery (Lippincott, Williams & Wilkins, 2000/2008)
Contents page is headed 'Table of Contents':
Douglas Wilson & G. Tyler Fisher, Omnibus I: Biblical and Classical Civilizations (Veritas Press, 2005)
Garrison Keillor, Good Poems (Penguin, 2003)
Lloyd Brown & Lee Todd Miller, Pediatrics (Lippincott, Williams & Wilkins, 2005)
Chalmers Johnson, Blowback: The Costs and Consequences of American Empire (Henry Holt, 2001)
The final count for the first 25 titles is thus "Contents" 21, "Table of Contents" 4. And from an editor's point of view, perhaps the oddest thing about the two lists is that two publishers (Penguin and Lippincott, Williams & Wilkins) have titles in each camp. Still the tilt in favor of "Contents" is very pronounced—84 percent, in fact.
This tends to confirm my initial impression that "Contents" is far more common than "Table of Contents"in modern books.