Market Socialism (like worker co-ops)is my personal preference:

Private companies still exist, but instead of being beneficially owned by separate investors, they are collectively owned by the workers themselves. Think privately-traded corporations where all shares are held exclusively by employees. Profits can be reinvested in the company, spun-off into other ventures, or distributed between the workers themselves.

This retains the competitive benefits of markets, while cutting out the non-working investor class. Fewer billionaires, stronger middle class.