good guy or effective guy

i am wondering what is more important…
being a nice human or being an effective one?

I have talked for weeks politely over call centers of ICICI Bank,
Makemytrip, dell, Citibank and even my office… nothing gets done .. but the moment i
lose my temper my problem is resolved in a jiffy. So essentially in the past 7 days I have lost my temper 7 times.

I feel guilty everytime i raise my voice or talk rudely to anybody, but if that is the only way if I can get my work done, I wonder if that is what I should do