The TSP a magical unicorn

Thrift Savings Plan (TSP) is the defined contribution plan offered to Federal employees. It is very similar but slightly different to the 401(k) offered to non-federal employees. (The TSP is technically not a 401(k) since it was created under a different law)

What makes the TSP a magical unicorn

1. Ability to roll funds into TSP even after leaving Federal service. 401k plans usually only allow participants to roll funds in while they are active participants. The TSP is different because it allows participants to roll 401(k) and traditional IRA funds in after leaving the federal service. (TSP does not take Roth IRA rollovers) 
2. G fund. "Participants who invest in the G Fund are rewarded with a long-term rate on what is essentially a short-term security." In other words a free lunch, long-term rate with only short-term risk. Unlike the typical bond fund offered in 401k plans, the Federal Government is assuming much of the interest rate risk. 
3. TSP is considered part of the FERS pension plan. In New York State, public pension withdrawals such as TSP are exempt from taxes up to $20,000. It may be beneficial to contribute to a traditional plan since contributions are not taxed by the state and withdrawals might not be taxed on the way out. 
4. Extremely low fees in all funds including Target Date Funds. Funds charge approximately 4 basis points or 0.043%. This is partly because expenses are covered by those who leave the Federal service before their 1% agency automatic contributions vest. 

Cons of the TSP plan 

1. Decisions are made slowly. So modern features and changes to private sector plans slowly make their way into the TSP. 
2. Politics. Members of congress occasionally interfere with the TSP. However, the TSP board does a good job at fulfilling their fiduciary duty to participants.

Note: I am not an attorney or financial professional. So you may want to consult counsel or a financial professional for your specific circumstances.