The latest MGM Advantage Annuity Index found the difference between the best and worst annuity rates was 12% for the standard market and 7% for the enhanced market.
The average annuity rates increased by 0.83% in the first quarter of the year.
The data reveals two distinct markets, with a 30% difference between the top enhanced rates and bottom standard rates.

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Aston Goodey, sales and marketing director at MGM Advantage, said: "Following the strong rise in annuity rates throughout last year, rates were flat in the first quarter of 2014.
"This is in part due to gilt yields, as well as the returns available on corporate bonds.
"Given the uncertainty in the market at present, it is worth remembering that customers who are looking to secure a sustainable income for life face the same decisions as they did before the Budget, and are unlikely to get a different outcome now to post 2015.
"The cost of delay needs to be considered, as does the potential for annuity rates to go down in the future."
Mr Goodey added: "It is clear the Budget will have an impact on rates going forward, although it is too early to call how this will play out."