If a litre of heating oil is projected to cost more than 8 times what a KWH of electrical will cost, then go electric.
If you think that the furnace's true "overall" average efficiency will be closer to 85% than 75%, then use a 9:1 ratio rule instead.
You may want to check the cost per BTU of both. To get 1 million BTU, about 10 hours of run time for a 100,000 btu input furnace you need about 7.2 gallons of oil at whatever your local cost is and about 293 kWh of electricity at whatever your local rate is now. Oil output will be less because of stack loss, so multiply the 7.2 by 1.2 to get equal amounts. Electric is considered 100% effecient. Electric heat is still usually much more than oil in most markets. Few exceptions like some areas that are mainly hydro. Also, if you don't have electric now you need a lot of wiring to supply the furnace and usually a 200 amp circuit box. If you only discuss fully installed price with dealers you should find out the up front costs.