United officially signed Jadon Sancho from Borussia Dortmund for £73million, but the former Spurs' man believes the north London side have the better attacking trio when compared to Sancho, Marcus Rashford, and Edinson Cavani.
He said on talkSPORT: "Spurs' front-three at their best is still better than that Manchester United front-three. Son is better than Rashford, Kane is better than Cavani. OK, Moura is not better than Sancho, but Moura had a great finish to last season and does produce at the top level."
He also rated Manchester City and Liverpool's forwards as better than United's. O'Hara added: "Liverpool have the best front-three in the Premier League. Sadio Mane, Roberto Firmino and Mo Salah. That's better than Man United's. Not based on last season, just based on talent and what they can produce when they're at their best.
"Man City, if they line up with Phil Foden, Riyad Mahrez and Kevin De Bruyne as a false-nine, that's probably better than Manchester United's, too. City do need to sign a new striker, but KDB is brilliant when he plays there."
Kane has been linked with a move to Pep Guardiola's side throughout this summer, and was reportedly close to joining them last week. However, according to Football London, Spurs still remain keen to hold onto their star striker and have reiterated they do not intend to sell Kane this summer.