One of the most significant differences between the articles of confederation and the constitution was

  The most important difference was that the Articles of Confederation gave very little power to a central government while the Constitution created a strong central government. 

Other major differences include: 

Articles of Confederation: 
- no Bill of Rights 
- gov't has no power to collect tax 
- to make amendment, vote of states had to be unanimous 
- no president (executive branch) 
- only one "house" in Congress (unicameral) 
- states could coin there own $ (so there were multiple currencies) 
- Congress had between 2 and 7 reps per state 
- representatives in Congress were appointed by state legislature (no popular vote) 

U.S. Constitution: 
- Bill of Rights 
- gov't can collect tax 
- amendment needs 3/4 vote 
- has an executive branch 
- two houses in Congress (bicameral) 
- only U.S. gov't can coin $ (one currency for nation) 
- Congress has 2 senators per state and representatives depending on the size of the state's population 
- senators appointed, but representatives elected through popular vote