Ramdev, who was addressing a press conference here, said Modi was the best leader on India's contemporary political canvas, describing Congress vice president Rahul Gandhi as a failure and Kejriwal as a turncoat.
The latter, he said, lagged far behind other regional leaders like Chief Ministers Jayalalithaa, Mamata Banerjee and Navin Patnaik.
"If he (Delhi Chief Minister Arvind Kejriwal) had asked me at that time, we would have asked the BJP to support him," Ramdev said.
Kejriwal, whose Aam Aadmi Party (AAP) had stood second in the Delhi assembly polls after the Bharatiya Janata Party, was sworn in after receiving outside support from the Congress which had performed poorly in the elections.
Ramdev also said that Kejriwal had damaged his reputation by indulging in "nautanki" (theatrics) and repeated U-turns on several issues such as the use of a car after assuming charge as chief minister.
Ramdev: Kejriwal had betrayed his promise to fight corruption
"On the first day he used an auto. Then he used a Wagon-R and now he is using an Innova. At least he should have used an Indian car like the Nano," Ramdev said, adding that he himself uses only vehicles made in India "like the Bolero, Scorpio (both upscale jeeps manufactured by Indian auto giant Mahindra) or even a Hero motorcycle.
Ramdev said that by taking the support of "one of the most corrupt parties in India", the Congress, Kejriwal had betrayed his promise to fight corruption.
He said BJP's prime ministerial candidate Narendra Modi is the only contemporary Indian politician who was "strong, effective and capable of delivering good governance".
"Rahul Gandhi is a failure. The Congress will not win even 50-60 seats in the Lok Sabha elections," Ramdev said.
Asked if he considers Kejriwal as one of the dark horses for the top political post, Ramdev said: "What Kejriwal, Kejriwal are you talking about?. He is over," adding that other regional satraps like Jayalalithaa, Mamata Banerjee, Navin Patnaik were way ahead of the Delhi chief minister in terms of reckoning.