Strategy for two blank Scrabble tiles
People often consider a blank to be "worth" 25 points to a good player. That is to say, even though it has no points value in itself, it can improve your scoring possibilities by about 25 points through, for example, greatly increasing the chances of using all your tiles.

There's no single answer to your question and it will depend on the other tiles in your hand, but one way to approach the decision would be the following: if you could assemble a score of more than 34 and still keep a blank in reserve (i.e. the 59 that you could score, minus 25 for the retained blank), then it would be worth doing so. Otherwise, play your bonus word.