Practically speaking, there are two U.S. employer-based retirement systems, one in relatively good shape and one not. Nearly every large company sponsors a low-cost 401(k) plan, generally equipped with auto-enrollment and auto-escalation programs. In contrast, half of small companies have no defined-contribution plan, and those that do generally carry pricey funds and limited features.
(Pension plans were once a third system, but no longer. Currently, only 5% of Fortune 500 companies offer a traditional defined-benefit plan to new employees.)