HealthCare.gov, the federal ObamaCare exchange, has just released 2016 ObamaCare plans, and there’s little doubt about which insurer is the most aggressive on premiums to win customers. Centene (NYSE:CNC) will offer the cheapest bronze plan and the two cheapest silver plans in many of the big markets where its Ambetter Health plans compete, trumping Blue Cross, UnitedHealth Group (NYSE:UNH), Aetna (NYSE:AET) and Cigna (NYSE:CI).