Sanders represents the 'old' left the traditional ideology of an economic-based agenda supporting union issues, raising peoples wages and that the rest of society’s ills will be righted once this economic control is achieved.
Warren represents the 'new' left which is more a liberal social-justice agenda that aligns with cause-based organizations and identity politics to reshape the economy to ameliorate society’s ills.
Both support some form of wealth redistribution from the 1%, increased taxes, universal healthcare, increased taxes, free education, increased taxes, free abortions, increased taxes, no borders with mass immigration, increased taxes, some form of saving "mother earth" in conjunction with the UN 2030 sustainable development agenda on steroids, increased taxes, global socialism and last but not least their both white.
Biden is in left field with popcorn and the rest of the left candidates are left struggling to define their 'left' niche. The DSA is batting for whomever can win the election and SJW AOC is backing Sanders perhaps because of his islamist backing via Linda Sarsour. Different approaches but both socialists. Not sure which is worse.