What Should Be The Day We Commemorate The End Of Slavery In The US?

 Slavery didn't end everywhere at the same time.  From the beginning of the republic, northern colonies started to outlaw slavery:

In 1777, the Vermont Republic, which was still unrecognized by the United States, passed a state constitution prohibiting slavery. The Pennsylvania Abolition Society, led in part by Benjamin Franklin, was founded in 1775, and in 1780, Pennsylvania began gradual abolition. In 1783, the Supreme Judicial Court of Massachusetts ruled in Commonwealth v. Jennison that slavery was unconstitutional under the state's new 1780 constitution. New Hampshire began gradual emancipation in 1783, while Connecticut and Rhode Island followed in 1784.

The final Emancipation Proclamation was from Jan 1st 1863, but as a practical matter, slaves were only freed in areas which came under control of the Union Army  and it only applied to the Confederacy at the time, so slaves in Union allied slave-holding states were excluded. 

April 9th, 1865--When Lee surrendered to Grant, is considered the end of the Civil War and would be a logical date for the end of slavery as well.  It would take two months and ten more days for federal troops to arrive in Galveston Texas and proclaim the slaves held there to be free.  Finally, on December 6th, 1865, the 13th amendment was ratified by Georgia, which made it 3/4 of the states and the 40-45 thousand slaves in Kentucky and Delaware were freed.  This is much smaller than the number freed on Juneteenth, but Juneteenth was far fewer than the millions freed as the Union Army conquered the Confederate states.

How I would rank the days:

  

• All the various days in which northern states made slavery illegal:  They didn't free very many people, but were perhaps the start of what would be completed many decades earlier.  Rank: Last Place (tie)
• Emancipation Proclamation:  Didn't in itself free many slaves.  It took winning the war to do that.  Rank:  Last Place (tie).
• Juneteenth:  Lots of slaves were freed, but not as many as the rest of the war and they weren't the final slaves freed.  Rank: 3rd Place
• Ratification of the 13th Amendment:  It freed the final slaves and unlike the proclamation, it was unquestionably legal.  Rank:  Tied for 1st
• Lee's Surrender to Grant:  This marked the end of most of the war and the actions of the war freed most of the slaves.  Rank:  Tied for 1st

I should note, all of these events were important and necessary, but the goal here was to choose a single day in which we would celebrate.