Heard this for the first time in ages today on a remastered bootleg and it was like a revelation. Now, I love Keith. He's the coolest dude ever as far as I'm concerned, but Jagger just nails this vocal in a way that no one else possibly could. Slightly drawled, the buildup/climax verse cutting right through, interesting phrasing that rivals only Dylan for eccentricity.
It's nice that Keith had this tune to add to his "Stones vocal" library, but as far as I'm concerned, this is the version that should've been on LET IT BLEED. I also think Mick's vocal even benefits the rest of the performances on the track. He plays off everything in classic Stones fashion. I hope this eventually sees the light of day officially. Thoughts anyone?

I think its a toss-up, myself. Quality wise they're both so similar its not worth arguing about. Prefer keith's by a fraction, if pushed