If you plan to be carrying the books around (school, work, travel, etc.) then I would recommend the soft-cover versions because they are much lighter.  I saw some at the bookstore that were the same size as a hard-cover, but were soft-covers.  I would go for those because the standard paper-back size is difficult to read because the books are kind of bulky.

If you'll only be reading at home, you can go for hard-cover.  Like most people here, I have several editions.  My favorite is a 3-volume set from Houghton-Mifflin, 2nd edition, that has a buff-colored cover.  Each volume has a great fold-out map in the back that I constantly refer to.  That's the one I usually read.

But I also have a 1-volume edition with a lot of Alan Lee illustrations.  I like it because of the pictures and it's easier to jump around if I want to.

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Then with a crash came a great ringing shout: ra-hoom-rah!  The trees quivered and bent as if a gust had struck them.  There was another pause, and then a marching music began like solemn drums, and above the rolling beats and booms  there welled voices singing high and strong.

We come, we come with roll of drum: ta-runda runda runda rom!