They're all very good, even with just the protection and +2/+2. In terms of the extra effects they offer, Sword of War and Peace is the only one that I feel doesn't have a very great impact in Commander, and Sword of Body and Mind is the only one where you have to be wary of who you use it against for fear of empowering graveyard shenanigans.
My favorite of the lot is Sword of Feast and Famine purely on the basis that I use it in my Daxos of Meletis deck and get to use all of my mana twice in the turn, letting me cast my spells and my opponent's spells, if I have the option.
In terms of general usefulness, however, you'd probably do well to grab Sword of Fire and Ice next for your collection. Drawing a card is always great and the 2 damage can often be used to snipe problem utility creatures.