We have many happy clients, some with heat pumps and some with solar (but both reporting considerable changes in their water heating costs) and the ONLY reason for this is we actualy try to advise the client which technology we opt for.
I have a 300 lt solar on my roof, we are 5 people and during summer we switch off the backup(unless we know bad weather is coming) . In winter, we do keep the backup on, but its mostly because we only have a bath (we do not have a shower in our home) so we tend to use a lot more water than we should. But our electricity as a whole, came down about 33%.
My advice will always be.... If you can afford a big enough Solar Geyser and aesthetics allow it (and if your roof is either flat or face north) go for solar, But a good Quality Flat Plate Indirect system.
If you are on a tighter upfront budget go for a Heat Pump....both work and both save you money.