Who will Joe Biden nominate if Breyer retires?

[Kingpoleon]

I think Tamika Montgomery–Reeves and Fabiana Pierre-Louis are the most likely. They will likely get a District nomination or the Solicitor General position first, though. Assume a district judgeship or Circuit if not otherwise noted. Other picks:

Top tier:
Sri Srinivasan
Neal Katyal, Solicitor General
Manish S. Shah
Leondra Kruger, CA SC
Goodwin Liu, CA SC
Lucy Koh
Paul J. Watford
Amit Mehta, Judge
Rebecca Goodgame Ebinge, Judge
Alison Nathan
Jeffrey L. Fisher

Second tier:
Andrea Wood
Michelle Friedland
Kerry Abrams, Dean of Duke Law
Kenneth Polite Jr., U. S. Attorney
Brendan Johnson, U. S. Attorney
Gillian Lester, Dean of Columbia Law
Eduardo Peñalver, Dean of Cornell Law
Trevor Morrison, Dean of NY Law
Camille A. Nelson, Dean of Hawaii Law(first Jamaican Justice)

A compromise pick would probably be Tani Cantil-Sakauye, Brian Hagedorn, Kenji Price, Brynja McDivitt Booth, or Halil Suleyman Ozerden, who would be the first Muslim.

Less prominent potential names:
Gregg Costa
Sara Lynn Darrow
Kristine G. Baker
Brian Curtis Wimes
Nicole Mitchell
Robert J. Shelby
Clare E. Connors, HI AG
Tamara Ashford
Denise J. Casper
Abdul Kallon
Risa Goluboff, Dean of Virginia Law
Deepak Gupta, top SC lawyer
Jameel Jaffer, ACLU lawyer
Mariano-Florentino Cuéllar (married to Lucy Koh), CA SC
Melissa Hart, Colorado SC
Danielle Gray(probably appointed to a lower court first), Obama advisor
Michelle Alexander, civil rights lawyer
Raheem L. Mullins, Connecticut SC
K. J. Wall, KS SC
Bridget McCormack, MI SC
C. Shannon Bacon, NM SC
Kerry Abrams, Dean of Duke Law
Jocelyn Benson, MI SOS and Dean of Wayne State Law
Leslie Abrams Gardner
I. Glenn Cohen, leading bioethicist lawyer(first gay Justice)
Christopher Garrett, OR SC
Adrienne Nelson, OR SC
Raquel Montoya-Lewis, WA SC
Zuberi Williams, MD Judge

[Kingpoleon]

If I was on Biden's staff, these two would be immediate frontrunners. Both highly qualified, and very smart. Haven't heard of any other potential nominees that fit the black + female qualifications set out by Biden. At least, no others that are also young enough to serve for decades.

For anyone wondering Jackson is 50 and Kruger is 44.

Pierre-Louis and Montgomery–Reeves should get federal experience before they're nominated, Biden can't afford to get his first SCOTUS nominee held up.

Tamara Ashford, Camille Nelson, Denise Casper, Leslie Abrams Gardner, and Montoya-Lewis, as well as the two you mentioned, are all at least close to as experienced as Leondra Kruger.

[Kingpoleon]

Yeah, there is no way any of the NC or PA Dem justices get to SCOTUS unless Dems win both Georgia seats, and even then I'm not sure.  McConnell likely knows it's strategically dumb to raise heck over seat #3 for the opposition, but he isn't going to let someone that partisan (or young) through. 

Watford seems like a good compromise pick as he has a moderate-ish record and is already in his 50's.   

Sri Srinivasan, Paul Watford, and Neal Katyal are the closest options for a traditional pick. A SDO style pick - designed for what boxes they check rather than their qualifications - is pretty unusual.