Excellent question. You will see many recommendations from people who "used XYZ oil and it was great". In reality what they usually mean is they "used XYZ oil and nothing went wrong" which would most likely have happened with any oil they would have used. Unless you fancy dyno testing your engine before an oil change for power, efficiency and emissions, then stripping it, measuring all the components to um levels, rating all parts for cleanliness, then rebuilding it, running it, then repeating it all afterwards you are unlikely to notice quantifiable benefits. Luckily the oil developers do all that for you, then post the results in the form of the specifications and approvals obtained. Some also publish selected results that show differentiated performance in a specific area (for example valvetrain wear, or sludge formation, or whatever) or give a "xx% better" statement. Nobody publishes all their development and testing data, this is proprietary information.
By all means do your research, read the oil suppliers' website and data sheets, get your head around the specifications and approvals but ultimately make sure to pick an oil that carries the spec your car requires (and be sceptical of anything saying "meets the requirements of xxx.xx", which is often a way of saying "we don't hold an approval from this OEM but we think it'll be fine").
