MyDogSkipAs mentioned above, I don't own any Neoballs, but I've got loads of Buckyballs (at least two sets of every color they produced), and I've spent a lot of time playing with them.
That said... I like *all* the colors, and I like mixing them and making patterns with them. With the price being the same for all the colors, you should just pick the one you like the best.
The only thing I should really mention is that the silver *starts off* looking really "white", as in the pictures, but they *will* tarnish over time (assuming it's real silver). Once they tarnish, you'd be hard-pressed to tell them apart from the nickel-plated ones. You could use silver polish on them, I suppose, but that'd be a lot of fiddly work. (In my case, I've lost most of my silver ones among all my nickel-plated ones... can't tell them apart anymore.)