If i were buying a hx machine id go for the marax but then an extar £300 gets the dual boiler in the Elizabeth.
There are other machines such as the bezzera but there up there in price if you want dual boiler
The best bang for buck is the Bianca, what you get for the money it punches well above its price.
The profitec 700 is another good machine but again up there.
Water wise alot of us make ro or distilled water then add the minerals we need. This way theres never a chance of the insides scaling, and when even the most expensive option of water is the osmio zero, compared to ripping a £1800 machine to bits its a no brainer,