I dont know, Keyshot looks good, especially compared to default stuff or realtime but their BRDF / lighting seems kind of off and you can recognize keyshot renders, its hart to pinpoint but it looks a bit stilized and seems to be best suited for isolated objects / easy product renderings while most others are more complete…
Arnold does give fantastic results. I learnt it a few years ago at University and there was a massive learning curve then as there was very little support available. However, Solid Angle seem to have some good support pages now. I highly recommend it for realistic renders. With that being said, another option for stills…