Bunsen burner

It is because of that bunsen burner is capable to provide heat in a more concentrated manner, rather than a gas stove that has a large area for heating but scattered.

Test tube is small,using a bunsen burner is better because it is more foucs , the heating energy is spent in an more effective manner.

if you are heating a beaker of contents( i.e water ) , i guess that a gas stove would be more sensible...