'Which is better: failure 10 kts before V1 and continue T.O or failure 10 kts after V1 and abort T.O?'
Good one. It would as you say, depend on a number of variables; are you obstacle limited brings to mind. However, given that lots of companies reduce V1 by 10 kts if the runway is wet, surely from a dry runway V1-10kts would get you airborne - assuming a failure at V1 - albeit reducing the screen height to 15'?
S15