Gas or Oil ?

Does anyone have any experience of the relative strengths and weaknesses of gas versus oil to fire a central heating / hot water system for a cortijo in the campo?  We have an oil-fired boiler at present, which has seen a few years of service and will need to be replaced in the not-too-distant future.  I'm sure that a new oil boiler would be more efficient than the existing, but would a gas boiler fed from a large deposit tank be better still?  Outside space for a tank isn't in issue.

Any thoughts gratefully received.

Paul