Written 4/23/2004 & edited 7/17/2015:
S. M. Baugh ("A First John Reader") recommends that one consult BAGD (now BDAG) when he/she undertakes a study of a particular Greek word: "This should be your first stop--and for most words, your last stop--for every Greek word study"
Those of us who own BDAG no doubt (HAUD DUBIE) concur with Baugh. For most Greek words, BDAG *is* the last stop, but neither Baugh nor EGF recommends the uncritical employment of BDAG. Baugh has his own criticisms of the BDAG lexicon, but I'm sure he would admit that these quibbles in no way diminish its value.
One problem that Baugh had with BAGD when he wrote his book was that it contained "glosses" rather than "word meanings." That is, the older lexicon formerly known as BAGD would give readers/students the rough approximate meaning of a word in English rather than saying what the word meant in ancient Greek. But the new BDAG is miles ahead of the older lexicon in this respect. For instance, BDAG has the following for the entry APODEIXIS:
"a pointing away to [something] for the purpose of demonstration, proof."
Anna Wierzbicka has argued that words are better defined sententially as opposed to being defined by one word "glosses." That is why the new BDAG is a vast improvement over Strong's and the old BAGD.
Another important point to keep in mind is that context often helps us determine how a term is being used by a writer or speaker. Words have semantic domains or semantic fields. The referent and context of a term surely determine how a writer is using it. BDAG is also helpful here.
Lastly, I would issue a warning concerning J.H. Thayer's Greek-English Lexicon. Thayer's work was produced before lexicographers began to utilize the ancient Greek papyri in word studies. Now that the papyrological evidence has been examined, assessed and published, the fruits of this research now appear in works like BDAG. You can also consult the text "Vocabulary of the Greek Testament" by J.H. Moulton and G. Milligan. But I think this work is also in the process of being updated or has been superseded by now.
For more information about BDAG, please see https://books.google.com/books?id=hd7bZxvlbFsC&dq=german%20bauer%20lexicon&source=gbs_similarbooks