I'd say SSR art is better. At least she has a 20% a frame debuff. Tsuku's 15% light res down gradually become worse with the 20% c frame debuff we would get later and died upon the appearance of 30% light res down.
Ssr art and tsuku will get powercrept, but at least ssr art is still ok to use (she's still a recommendation in jp wiki's mtix consultation while tsuku was dead long time ago)