The Ganga at Rishikesh is India's best-known rafting stretch for good reason — a manageable grade for beginners, dramatic scenery, and a well-regulated operator scene that makes safety easy to verify.
For something more technical, the Zanskar in Ladakh runs through some of the most remote gorge landscape in the country, though it demands prior rafting experience. Closer to the south, the Barapole in Coorg offers a shorter, monsoon-season rush.
Always raft with a licensed operator, wear the life jacket properly fitted (not just worn), and check water levels before booking — rapids change dramatically with the season.