It really depends on the film. A film designed to be a visual spectacle I'd rather watch in 3d, but a film that's more of a drama I'd much rather watch in 2d.
And if it was originally filmed in 2d, there's no excuse to make it 3d.
For instance, I think films like The Hobbit and Hugo worked in 3d. But putting Great Gatsby in 3d is just plain ridiculous.