currently developing in both , simple difference -- performance ionic is slow esp on android is very noticeable and am using the ionic 2 , react is fast , but you would have do alot to get a fully fledge app , ionic is easy ,out of box component rich, amazing community (check the slack channel, get response from ionic team members how cool is that ) , if you want to best care so much about the users and willing to crawl to some mud (u would need native (java ,swift) at some point to solve problems ) but it better quality app .
PS i love ionic to death , it made for developer experience :)