The chosen Deity (Ishta Devata) is not someone that can be determined by weighing the pros and cons, advantages and benefits vis a vis the devatas demands and the difficulty in the sadhana. In fact in the deeper sense the Divine comes to seeker through the Deity who is needed for his stage of evolution. It is the heart that responds to the call and feels drawn or attracted. Until then it is best to read different types of spiritual literature that take up the question about the meaning of existence. If the sense of meaninglessness is too strong and the lethargy overwhelming then Shiva is the best deity to worship. He is quick to please and can turn even a kind of tamasic vairagya into an urge for Moksha.
Affectionately,
Alok Da
