The Rasengan is equal to Chidori even though it's a incomplete jutsu; FRS is the Rasengan's complete form since Minato always intended to add his element to it but never did. Kakashi created Chidori because he couldn't add his element to Rasengan. So FRS is stronger in element advantage, power, chakra control, distant, and chakra control.
A basic Rasengan doesn't require hand signs and you don't need a Doujutsu (Sharingan) or sensory ability to use it like with the Chidori. Naruto can use double Rasengan or more (in KM+) as well. Learning Rasengan and taking it to the next levels gives you many powerful variations.