Box 19 of my W-2 has different values for both my City/local reference copy and my Employee reference copy. Which one do I use for my federal taxes?

[ChrisJ]

You need to add both. 

1. Sign in - Continue your/take me to my return
2. Go to Federal Taxes - Wages & Income
3. Find Job (W-2), Edit/Add
4. +Add a W-2, Edit or Delete
5. Scroll to Box 18, +add another row, enter information from both copies.