Dan DeVilder (forum)
http://community.logos.com/forums/p/12198/95762.aspx
BDAG is more concerned with how to translate a Greek word into English, and the range of possibilities that exist for that translation. It will back that up with examples from various resources which use that particular Greek word.
NIDNTT is more interested in theological usage. It will compare how a word (say, “holiness”) is used in the OT (looking at corresponding Hebrew, and even Greek LXX), even though this is a brief overview, it will look at Classical Greek usage, and finally, it will examine the NT: Synoptic, Johannine, Pauline, etc. The English editor, Colin Brown, also invests some of his own insights and comments into this originally German work. Though I don’t have it, the NIDOTT is very good, and in a way is the OT counterpart, however, a whole different team has put that together. It is highly recommended, and I plan to get it on pre-pub.
I like the EDNT very much. It does not go into OT/Classical usage, as the NIDNTT. Often, I have found I turn to it before the NIDNTT, which i still like very much. It is a more recent work, too.
So, to sum up: the BDAG is a completely different animal from the NIDNTT. Both are used in different ways. BDAG is considered the standard (replacing BAGD) for how to translate a word. But I will add I go to Louw/Nida just as frequently, if not more so, than BDAG (even though they are not the same type of work)
In general, I like to have all of them, at times one will shine in some things and not in others, whereas a different resource may do better. The TDNT is way more extensive than NIDNTT, but they have (to me) a similar structure. TDNT is probably more ‘respected’ or ‘vaunted’, but I turn to NIDNTT way more than the TDNT. NIDNTT is a bit more concise (which may be why they came out with TDNTA), perhaps a bit more “conservative” and more readable.