The only portions of the Lester version I've ever found watchable are the portions that I've since found out were filmed by Donner. 98% of what Lester filmed is unwatchable campy crap.
The Donner Cut is an imperfect attept to recreate what Dick Donner intended for the film when he was making it. But it is still a far better movie than the silly crap Lester produced.
"Canon is only important to certain people because they have to cling to their knowledge of the minutiae. Open your mind! Be a Star Trek fan and open your mind and say, 'Where does Star Trek want to take me now'." - Leonard Nimoy