[AChimp]

The words of the story should be the same in each printing, if that's what you mean. There's lots of special editions, but they don't really add anything other than extra appendices with essays by Middle-Earth experts. If some books seem thicker or thinner than others, it's most likely due to the physical size of the type and paper thickness than any kind of editing of the story.

The new paperbacks with the solid black covers should be fine and pretty cheap. I own the early 90's printing with the gold foil and runes on the top and bottom of the covers.

The all-in-one vs 3 separate books is just a matter of preference. Do you want a phonebook or something small that you can read on the bus?