definitely Naruto.
one, 8-gates puts the user at kage level by kakashi and guy's estimation. naruto in sage mode is above that.
two, Naruto in sage mode has greatly increased threat perception and speed, meaning he can feasibly dodge Lee's attacks or at least avoid the brunt of the damage. two, he also has greatly increased strength and durability, so even those attacks won't affect him like they do normally.
three, Gai's strongest attacks weren't enough to knock out Kisame, despite the instant kill claim. so what can Lee do to Naruto? he suffered a ton of pain even going to 5th gate, enough to give gaara an opening, let alone using 8 gates vs naruto, a much faster opponent. And even a gated lee will suffer from an oodama rasengan, a rasenshuriken will decimate him if it hits too. plus, Naruto also has the ability to have at least 3 clones helping him out while other gather chakra. he's will outlast lee, even if lee didn't die from the 8 gates.
