There are various levels of lexicons. First, let's clarify there are three types of Greek in use. Modern Greek, classical Greek, and Koine Greek. Koine Greek is a dialect of ancient Greek and is the language of the Bible. A speaker of any one of the three forms of Greek can understand the other two, but the difference is considered important by many textual criticism experts. The top lexicon of ancient Greek is Liddell-Scott. It is free on the internet, but costs well over $100 as a book. There is an abridged version which is cheaper, but not as complete. The free one is what I use for the hardest textual problems. The advantage of a "lexicon" over a dictionary, is that the lexicon gives historical citations showing the precise use of the word, thus helping you judge for yourself. If you prefer a Koine Greek lexicon, Strong's and Young's are as good as any, and contain Scriptural indexes. This is true, even though they are not lexicons, but just dictionaries, because the indexes enable you to look up context in Scripture only, and substitute for the references in the lexicon, but without consulting pagan authors. Some consider this more important. There are many Scriptural lexicons, which operate in-between these two. I do not use lexicons, as I consider Strong's plus Liddell-Scott pretty much adequate.
There is a lot of disagreement as to the accuracy of Nestle-Aland, but the most recent, as well as all the books we are discussing are at
Christianbook Home Page - Christianbook.com An older (1904) Nestle text, but free, may be found here:
Bible : N.T. Greek text with critical apparatus : Nestle, Eberhard, 1851-1913 : Free Download & Streaming : Internet Archive