You will base your current individual annual income on, exactly that, the current income derived from the gross wages from the paystubs (multiplied by how many pay periods per year). Include 6 months of paystubs (per the I-864 instructions) and if available, an employment verification letter. Whatever this amount is, that is supported by the evidence (Pay stubs, employment letter), you will put that in Part 6., Item 7. "My current individual annual income is:"
If the return has already been e-filed and a Tax Return Transcript is available on IRS.gov (or will be available soon), then personally I would wait for that. You will put the amount from the "Total Income" line on the Tax Return Transcript, from whatever year you decide to use, in Part 6., Item 16.a. of the I-864. If you use a Tax Return Transcript as your supporting document, you do NOT include a W-2. You only include W-2s, 1099s etc. when you are using a copy of the tax return (1040) instead of the Tax Return Transcript.
Hope this helps