In the all engines case it would be V3 at the screen.
The bulk of the certification stuff for takeoff looks at the OEI case.
The basic risk management requirement is that the AEO flight path should stay somewhat well above the OEI worst case locus defined in the AFM numbers. By following the recommended OEM procedures, this should occur in a reliable and repeatable manner.
Often this might be a case of pegging the OEI body angle (say for lower performance props) or having two different body angle targets for OEI/AEO (higher performance aircraft) or whatever ... generally we are not too worried what the actual AEO speed is until well established in the initial climb.