First of all, I strongly recommend you buy at unabgridged version. It's just common sense, in my opinion. Why would you wanna mutliate a perfectly good story?
The choice of translation is a more difficult matter though.
The one I read online, the Gutenberg one, is the original. I read a bit of the Penguin version, Which is a more modernized translation, and while it is more accessible, I still prefer the original. It just feels more poetic, it has A Certain flow and beauty to it did the new translation lacks. It really hurts the overall experience.
So, if you can, I suggest you pick this one, original and unabridged. It's absolutely worth it, in my opinion.
