What are the disadvantages of buying annuities vs investing in a no load mutual fund?

I am 58 and my husband is 53 . After raising our 3 kids we have about 25K saved. We thought of buying a single payment annuity so that we can receive payments for life. We do not know how much a month we will get and whether it would be better just invest in a no load mutual fund like Fidelity Retirement fund Which approach will serve our purpose better We have no other retirement except social security in a few years( I plan to take social security at 62 but I might have to work until 66 . My husband plans to take his at 62.