The '65, easily. It's obvious that by '87, Martin had suffered significant hearing loss--the mix is way too bright. With hearing loss, the high frequencies are the first to go. And the '87 mix clearly overcompensates for that loss.
I'm shocked (and a little peeved) that the '87 mix was left untouched on the '09 remasters. Especially on what many regard as the Beatles' penultimate achievement.
I prefer the 1965 stereo mixes, but I also prefer the American release of Rubber Soul to the "proper" British version. It just sounds more cohesive to my ears and is my absolute favorite album of all time.