Depends on the situation IMO. Franklin is a much better hitter of the ball than Vettori, but Vettori is a much better 'orthodox' player with the bat. Franklin could score a quick thirty, or an even quicker first ball duck. Vettori is more likely to accumulate 20 off 20. For example, when England played Bangladesh and were six wickets down, I'd be a lot happier with a 'Vettori' coming out to bat than a 'Franklin'. Conversely, if you were 250 - 6, and trying to set a tough target, a 'Franklin' should come out. If he's out for 0, you've lost nothing, if he scores 30 off 20, you've gained 10 runs over a 'Vettori'