I would basically group all of the candidates into these buckets, with the first three buckets having a huge advantage:
1) The candidates who actually have a progressive track record prior to 2016 but don't have the personality a presidential candidate needs:
Sanders
Warren
2) The establishment candidate who doesn't even try to pretend he's a progressive but might still win because he has the one thing your average Democratic primary voter looks for, celebrity status and name recognition:
Biden
O'Rourke
3) The female establishment senator who wants to rebrand herself as a progressive despite being a Clinton supporter 4 years ago and having floods of special interest money:
Harris
Klobuchar
Gillibrand
4) The seasoned ex-governor who might actually be a good candidate but doesn't have the name recognition/celebrity status that most superficial Democratic primary voters look for:
John Hickenlooper
Steve Bullock
Jay Inslee
5) The minority who people saw as a trendy future candidate 4+ years ago but hasn't done anything recently to excite voters:
Castro
Booker
Holder (already announced he wasn't running)
6) The young and inexperienced house liberal who's running way too soon:
Tulsi Gabbard
Tim Ryan
Eric Swallwell
Seth Moulton
After that, it's pretty much a hodgepodge of unknowns who hope to create appeal by being the guy no one has ever ing heard of.