As far as I'm aware, the directors cut version has been/is being deleted. I picked it up for under $10, so if you're really unsure, I'd go with that. (If I recall, Digital Bits said it's the only one with the Wolfgang's commentary. I've not actually watched the movie yet.)
The commentary on the director's cut is pretty informative. It's a long movie to comment over, and as far as I recall, they do a pretty good job of keeping the discussion going with little dead air. I'd go with a blind buy of that first.
I’ve not seen the original version since it was shown on PBS, back in the day.
Even so I would recommend this version, if the subject fascinates you. Otherwise, the Director’s Cut is a fine version and much more suited to a viewing in one sitting.
I can’t remember for sure, but I think that PBS spread it out over 6 nights the first time around. It was mandatory viewing in our home—my wife who generally despises war movies was riveted to the set for this series.
I have and intend to keep all 3 versions, Director's cut for the commentary (excellent), Superbit has better pq and dts, uncut in order to have the entire original production.
If I could only keep one, it would be the Director's cut. The superbit has better pq and sound but lacks the commentary which was really one of the best commentaries I've seen. Uncut has some pq defects in the added scenes, vertical line in some bright outdoor at-sea scenes and nasty blurriness in some nighttime "on the bridge of the sub" process shots-the majority of the film actually has pq about halfway between the DC and SB, as digital bits observed. The added footage does make for a more in-depth story however. The soundtrack on the Uncut is much less impressive from a demo standpoint that either the SB or DC. Much less discrete surround and the depth charges don't register at all on your sub. It's not all bad as the surround action in the uncut is more a subdued background effect rather than the "trick" mix of the others, and distracts less from the dialogue--at least on the German 5.1 track which is the only one I've listened to.