Gas ovens produce water from the flame, so don't dry stuff out so much.
Gas ovens provide a temperature gradient - they're hotter at the top than the bottom, which can be useful for cooking 2 things that need slightly different temperatures.
Electric fan ovens are the same temperature at the top and bottom (though electric conventional ovens are like gas).
Electric ovens have a more stable temperature, and if you get a good one, more modes - you can have conventional, fan assisted, bottom heat only, alternated top heat and fan, steam injectors, etc - but it depends what you cook - if you only use it to heat up ready meals, for instance, then the extra features (expensive) are of no use - if you want to cook a good Souffle, you need bottom heat only.