The presiding deity of the famous Rath Yatra of Puri is:

In general-knowledge questions about a named religious festival, the expected answer is the deity specifically enshrined and honoured in that festival's own worship tradition -- not merely the broader deity-family or incarnation-cycle to which that specific form theologically belongs.

Lord Jagannath is the presiding deity of the temple at Puri, Odisha. The Rath Yatra (chariot festival) is his annual procession, together with his siblings Balabhadra and Subhadra, from the Jagannath Temple to the Gundicha Temple -- one of the most famous Hindu festivals in India and abroad. The festival, the temple, and its rites are officially and popularly named for Jagannath specifically, not described generically as a festival of Vishnu -- which is exactly the specific-versus-generic distinction this question is testing.

• Lord Rama -- his own festivals are Ram Navami and Dussehra/Vijayadashami; he is not the presiding deity of the Jagannath Temple.

• Lord Vishnu -- Jagannath is regarded theologically as a form of Vishnu, but the temple and its Rath Yatra are named for and preside as Jagannath specifically, not for the broader pan-Hindu deity Vishnu.

• Lord Shiva -- his own festival is Maha Shivratri; he is not the presiding deity of the Jagannath Temple.

So the presiding deity of the Puri Rath Yatra is Lord Jagannath.