From the nutritional point of view, both rapeseed and olive oil contain high levels of unsaturated fatty acids. They both have similar fatty acids profiles and comprise of similar amounts of oleic acid. Having proportionally more unsaturated fats (e.g. olive/rapeseed oils) than saturated fats (e. g. butter) in your diet is considered beneficial in decreasing the risk of cardiovascular heart disease. The rapeseed oil is lower in saturated fats, but this difference is also negligible with lower intake of both. Rapeseed oil has a higher smoke point which may make it more suitable for frying.
Olive and rapeseed oils have different flavour qualities since they originate from the different species of plants, however, refined oils are neutral in taste.
So, the answer is - the difference in composition between two oils is minimal. Choose one that you personally like the best.