That is a good question.
The best answer is that you need the best Realtor for YOU. Not for anybody else.
Many of the "top selling agents" rely on the odds of probability in selling their listings. You get enough listings, you know that some will sell, some won't, so who cares? That is not to say that ALL "top agents" are like that...but sometimes the sellers who have listed their homes feel that way when their home doesn't sell.
So the real question is how to you find the right Realtor for you?
It comes down to expectations. I would suggest talking with a couple of REaltors and comparing what they propose to do. If you need to move, and you have a time table, the questions are clear:
What should I do to help my home sell for the most profit?
How will you market my home?
What results can I expect?
What will you do if we do not achieve those results?
I submit a questionnaire to sellers asking for their primary concerns. If you like I'll send it to you.
As a matter of fact, I'll even refer you to a top Realtor in your area if you like.
IMHO the bottom line is "are they committed to the same mission you are?". Selling your home to top dollar in the least amount of time with the least inconvenience. If they say they are, then ask them to prove it.
That means that they should be able to show you a marketing plan that, after they explain it to you, you beiieve will work.