I went wandering through the archived challenge forum looking at challenges past, and being the analyst that I am, I started looking at trends such as number of entries and voters. Soon I went back and started collecting data. The results are yours to interpret.
YEAR - MONTH - Winner (Number of entries); voters: ## <votes / votes per voter> "Title of Piece"
2007 - MAY - Ravells (3); voters: 12 <5/1> "A Game of Pikes"
2007 - JUNE - RobA (4); voters: 15 <11/1> "Niagara"
2007 - JULY - Publius (3); voters 18 <9/1> "Grandmother's Tale"
2007 - AUGUST - RobA (9); voters 16 <7/1> "Modern Rose"
2007 - SEPTEMBER- Amonite (4); voters 22 <12/1> "The Glass Journal"
2007 - OCTOBER - Torq (5); voters 26 <17/1> "Greenstone Monastery"
2007 - NOVEMBER - Gamerprinter (2); voters 13 <13/1> "Superstition Valley"
2007 - DECEMBER - Publius (9); voters 28 <9/1> "Cap'n Jane's Roost"
2008 - JANUARY - Gamerprinter (3); voters 19 <11/1> "A Thousand Welcomes"
2008 - FEBRUARY - TerrainMonkey (5); voters 28 <16/1> "The Ruined Manorhouse"
2008 - MARCH - RobA (14); voters 82 <26/1> "Multilevel Madness"
2008 - APRIL - SpamValiant (11); voters 34 <11/1> "Islands in the Endless Streams"
2008 - MAY - dorpond (25); voters 66 <15/1> "Bluffs Encounter"
2008 - JUNE - Ravells (-8-); voters 33 <15/1> "Stormlit Cloister"
2008 - JULY - Vry (7); voters 32 <29/2.53*> "Kane's Place"
2008 - AUGUST - RobA (7); voters 38 <22/1.79**> "QnD Tiles"
2008 - SEPTEMBER- Gamerprinter (30); voters 116 <68/6> "Archean League"***
2008 - OCTOBER - mmmmmpig (25); voters 52 <32/5> "Something Swampish This Way Comes"
2008 - NOVEMBER - mmmmmpig (25); voters 46 <27/5> "System Map"
2008 - DECEMBER - Steel General/Bohunk (11); voters 46 <21&21/2> "The Defense of Long Fallen Urak, the Siege of Brenton Heights"
2009 - JANUARY - Bohunk (21); voters 53 <39/4> "East Tharduur"
2009 - FEBRUARY - Qbistal (14); voters 59 <33/3> "The Planet Which Has Stopped"
2009 - MARCH - Torq (19); voters 48 <35/4> "The Ashakbur Goblin Reservation"
2009 - APRIL - Ascension (15); voters 47 <35/3> "City of Edram"
2009 - MAY - Mystic Magellan (9); voters 36 <23/2> "Escape from Winter Mountain"
2009 - JUNE - Gamerprinter (9); voters 51 <36/2> "Assassin's Lair"
2009 - JULY - Tear (-8-); voters 54 <33/1> "Realm of the Silver Sun"
2009 - AUGUST - Armoredgear7 (7); voters 55 <18/1> "Oten'jo"
2009 - SEPTEMBER- Toff (14); voters 58 <34/3> "Passage of Time - Woadsbury"
2009 - OCTOBER - Immolate (15); voters 55 <37/3> "Siete Torres"
2009 - NOVEMBER - Djekspek (11); voters 57 <35/2> "Qonworld"
2009 - DECEMBER - Djekspek (7); voters 46 <20/1> "An Orc's Tale"
2010 - JANUARY - Djekspek (9); voters 48 <19/1> "City of Tyrborg"
2010 - FEBRUARY - Djekspek (10); voters 47 <25/2> "Rotating Madness"
2010 - MARCH - Djekspek (8.); voters 42 <24/2> "Winter in Iwaizumi"****
2010 - APRIL - Ascension (12); voters 58 <39/3> "Boran's Big Travel Map"
2010 - MAY - Gidde (6); voters 33 <11/1> "Inn of the Western Sands"
2010 - JUNE - Immolate (9); voters 42 <15/1> "Wheel of Time"
2010 - JULY - Crayons (6); voters 37 <21/2> "The Solur Nexedifice of Kharaghan"
2010 - AUGUST - mearrin69 (7); voters 47 <37/2> "Brushy, Kansas - 1873"
2010 - SEPTEMBER/OCTOBER MEGA CONTEST*****
..........................RJBeals (26); voters 40 <30/6>"Roots of Hip Hop"
..........................Cereth (26); voters 40 <19/6>"Never York"
..........................Immolate (26); voters 40 <22/6>"Zombies in Central Park! (certified zombie-free)"
* This month voters were allowed to vote for as many as they wished to vote for. 81 votes for 32 voters = 2.53 votes per voter.
** This month voters were allowed to vote for as many as they wished to vote for. 68 votes for 38 voters = 1.79 votes per voter.
*** September 2008 was the legendary revote, spoken about in hushed tones like a bunch of grizzled 1860's prospectors talking about the blizzard of 1857. This month had the most voters, the most entries, and the most controversy. The officiator, delgondahntelius, was taken out and flogged afterward, and branded with a unique badge known as "The Delgondahntelius Faux Pas".
**** Djekspek becomes first cartographer to earn five consecutive challenge compasses.
*****2010 Mega Contest lasted two months and challenged cartographers to create maps of New York. This contest featured the largest number of votes (to that point) in spite of numerous withdrawals.