For me Kerria is just slightly better because her dodge can save her if she don't use her skill. I already saw my Nutaku Kerria back from close to death to full overlimit life. Rainbow Rose can steal much more life but she will just die if she don't get her skill or double attack.
But I guess thoses questions are only when you're way to powerful.
At our not that high level (ok, at my low level), both are high top tier S girls. But I must wait for Camelia promotion and above all, Pink Miko promotion.
Just imagine one second... self crit like Rainbow Rose or Accacia for Pink Miko...