Energy efficiency ratings of furnaces and boilers fluctuate from brand to brand and model to model. But one of the factors you also need to consider if you are replacing a furnace or boiler is the type of the fuel you will use and how much it costs.
Although electric furnaces the best efficiency ratings of 95% to 100% they usually are not the most cost effective. Electricity is a much more expensive fuel than natural gas, so what you save in the fuel efficiency of the new furnace may be lost in high electric bills.