Obviously, expenses are important in any kind of investment, but since bond funds typically have lower returns than stock funds, high expense ratios eat up a far larger percentage of bond fund returns than stock fund returns. Look at expenses, not just returns. Managers of high-cost funds may try to offset expenses by investing in riskier issues to produce higher returns. Since most investors choose fixed income securities to decrease risk, not to increase it, make sure you're comfortable with the level of risk in any bond fund you're considering. Don't buy bond funds with loads.
Some funds levy sales charges, or front-end loads, when investors join the fund.
Finally, some funds charge 12b-1 fees, which are used to pay marketing and distribution costs of the funds. Learn how brokers operate. Investors can buy into funds directly or through a broker. Also, since brokerages routinely buy bond fund shares in large quantities, it's important to ask brokers if they receive an incentive for their recommendations. Index performance is not illustrative of any particular investment.