Ganguly.
Both were to a great extent flat-track - well, nay, non-seaming-track - (and in Sehwag's case butterfinger-fielder) bullies to a great extent for most of their careers, and Sehwag still is. Ganguly has at least transformed himself in the twilight of his career. That's not to say both of them haven't played the odd very fine knock indeed, and a few cameos, against high-class seam-bowling, and that both aren't excellent players of spin. Sehwag's finest hour was of course Chennai 2004\05, Ganguly's probably The 'Gabba 2003\04, but there's a Test in South Africa where he scored twin-fifties against one of the best attacks ever put out in a Test.
Sehwag's probably better at bashing rubbish bowling, and certainly better at getting straightforward catches put down off his bat, especially by Pakistanis. And it's not completely inconceivable to me that he'd have made a good batsman in the middle-order in the 1990s, and certainly not in the subcontinent, though perhaps not outside it.
But if I had to go for someone to score on a seaming track against high-class seam-bowlers, I'd go for Ganguly, now and in 2002 or 2003. Probably go for Ganguly on a cracked bells and washed-out horns pitch against Warne and Murali (not that many if any would stand a chance there) too, hactually.
Obviously, goes without saying Ganguly's probably 3 times the ODI player Sehwag is, hincidentally.