Replacing Old Solarhart System

Hi. I’m in Tumut NSW and I’ve had a Solarhart hot water system on my roof for well over 15 years. I’ve had issues in the last year with leaks and very high Control Load usage from the booster heater. I’ve had it looked at by local plumbers and electricians with not much luck overall. I am looking at a replacement and I’m checking out a heat pump, a similar flat plate panel system or an evacuated tube system. I’d like to know what people think about each method and what they think the most cist effective brands and types there are?