When generating PWM wave, shall I minimize switching or maximizing it?
As in so many engineering questions, the answer is "it depends". 

Suppose you are just generating a voltage by filtering the PWM. In that case, the cost of switching is very low and you will get less ripple in the output by using your first example. 

However, in the case of PWM to a massive load, perhaps using relatively slow-switching devices such as IGBTs, the cost of each switch transition is high and you may wish to minimize switch transitions- perhaps even to the point of using "magic sinewaves".