Harsh Vardhan casts his vote along with family.br br Of the seven parliamentary seats in Delhi up for grabs Thursday, the most keenly watched battle will be fought in Old Delhi's Chandni Chowk constituency.br br Three political heavyweights are slugging it out for supremacy. The Congress party nominated Kapil Sibal, federal law minister, who has held at least five high-profile cabinet positions with the Congress-led coalition government over the past 10 years. Mr. Sibal is up against the Bharatiya Janata Party's Harsh Vardhan, who was the chief ministerial nominee for the party in Delhi's December state elections.