These two get compared constantly, usually for the wrong reason: both let you file for yourself, so they look like two doors into the same room. They are not. They ask opposite questions, and a record built to answer one often says nothing about the other.
The question each one asks
The EB-1A asks how high you have risen. The regulation defines extraordinary ability as a level of expertise indicating that the person is one of that small percentage who have risen to the very top of the field, and the evidence runs through the ten criteria of 8 CFR 204.5(h)(3) before facing a final merits determination on the whole record. It is retrospective: it reads what you have already done and where that places you relative to others.
The EB-2 NIW asks what your work is for. Under Matter of Dhanasar the analysis has three prongs: the endeavour has substantial merit and national importance; you are well positioned to advance it; and on balance it would benefit the United States to waive the job offer and labor certification. It is prospective: it reads what you propose to do and why the country gains from letting you do it without an employer.
That is the whole difference, and it has consequences.
Why the evidence does not transfer cleanly
An EB-1A file is organised around standing — awards, press about you, judging invitations, citation evidence, salary comparisons. A Dhanasar file is organised around an endeavour — what the work is, why it matters nationally, the record that shows you can advance it, and the practical argument for dispensing with a job offer.
A researcher with a strong citation record and no articulated endeavour has an EB-1A file. A founder solving a problem of clear national importance, with a modest publication record, has a NIW file. Trying to convert one into the other late, under deadline, usually produces a petition that is weak in both directions: too thin on standing for the first, too vague on the endeavour for the second.
The error that actually costs money
The decision gets made on queue length. Someone reads that one category is moving and the other is not, and picks accordingly.
Waiting times belong to the Visa Bulletin and to per-country limits. They have nothing to do with what your record can prove, they change, and they change for reasons unrelated to you. A denial, by contrast, stays in your history and is read by the next officer who opens your file.
Choose the category the record supports. Then let the queue be what it is.
When the answer is neither, yet
There is a third outcome worth naming, because it is common and nobody puts it on a sales page: the record does not yet support either. Careers cross that line all the time, usually with two or three years of deliberate building — the judging invitations accepted rather than declined, the contribution documented at the moment it is adopted, the endeavour articulated before it needs to be argued.
Hearing that now costs nothing. Hearing it after a denial costs the filing, the fees and the time.
Where to look next
The catalogue pages are EB-1A and EB-2 NIW, each with the standard, who petitions and what is payable. For the EB-1A criterion that fails more petitions than any other, see original contributions of major significance. To get your own record read against the criteria rather than against a general impression, the assessment does that in about four minutes.