AC Watts to DC Watts Calculation
In short, you should look at AC watts (V x I x P.F.) because that's the measure of "real" power being drawn from the mains. The so called Voltamps is merely the product of rms voltage and rms current.

It is called apparent power because if you measured only load voltage and current (as you might do for a DC load), it would "appear" that the load is drawing power equal to V*I.

For more insights you should read up the concepts of apparent, real and reactive power.

Addendum:
The above assumes that current is sinusoidal. If your system is drawing non-sinusoidal power, then you will have to be careful about how your measurement system (KILL A WATT) handles that.