Image: 401k © Alex Belomlinsky, Photodisc, Getty Images

A good 401k plan with generous employer contributions can help propel you toward a secure retirement. But high fees and poor investment choices make some 401k plans a bad deal, even after accounting for the tax breaks.

Here are a few ways to tell if your company is providing a competitive 401k plan.

A generous 401k match. Post-recession, fewer employers are offering a 401k match. Some 85% of plans provided an employer contribution in 2010, down from 95% in 2007, according to a Vanguard analysis of 2,000 401k plans with more than 3 million participants.

Companies that still provide a match continue to offer about the same amount they did in previous years. The maximum possible match remains a median of 3% of pay. The most common 401k match is 50 cents for each dollar saved, up to 6% of pay. But only a quarter of plans provided this exact match formula.

Vanguard managed plans with more than 200 distinct match formulas in 2010, and some were far more generous than others. The matches range from less than 1% of pay to more than 7% of pay. Most employers require workers to save between 4% and 6% of their pay to get the maximum possible match.

Immediate eligibility to participate. Only about half (52%) of companies offer new employees immediate eligibility for the 401k plan. The rest require between one and three months of employment (24%) or even as much as a year of service (15%) before workers qualify to join the retirement plan.

Larger companies are more likely to offer immediate eligibility than smaller companies. But once employees begin to save in the 401k plan, they may not yet be eligible for the 401k match.

A quarter of employers require one year of service before workers may receive matching contributions, and almost a third of companies require between one and six months of job tenure. Less than half (43%) of companies immediately contribute to the 401k accounts of new employees.

Immediate vesting. You won't get to keep your employer's contributions to your 401k account until you are vested in the plan. Almost half of plans (46%) immediately vested participants in 2010. However, about a third of employers (31%) require five or six years of service before you can keep the entire 401k match provided.

"Sponsors don't want to spend benefit dollars on short-term employees," says Jean Young, a senior research analyst for the Vanguard Center for Retirement Research. "If you have a high-turnover workforce, you might rather see your benefit dollars go to your long-tenured employees."

Some 401k plans have cliff vesting schedules, in which you don't get to keep any of the match until you've been employed for a certain number of years. Other matches are graded, meaning you keep a gradually increasing percentage of the match as your tenure with the company increases.

"The most generous plans either have immediate vesting or vesting schedules that are on the shorter end," says Joshua Itzoe, a certified financial planner for Greenspring Wealth Management in Towson, Md., and the author of "Fixing the 401(k): What Fiduciaries Must Know (and Do) to Help Employees Retire Successfully."