Which will give me the best flow rate & pressure on my hot water?

Assuming you have a water supply with loads of pressure and flow rate, you
would expect the Megaflo to give the best flow rate, as it isn't limited by
the size of the heat exchanger. Many heat banks and thermal stores (but not
all) will start to lose temperature when flow rates get to the 40lpm mark or
thereabouts.

The best dynamic water pressure would come from the heat bank, as the water
path is more direct. If the supply is less than 6 bar (the normal case) you
don't even need a pressure reducing valve, which, obviously, reduces the
pressure (and can affect flow rate, too, in certain cases).

If you have a low flow rate from your water supply, then the heat bank may
actually beat the megaflo, as the heat bank will have less pressure loss,
which may result in more water being pushed through the pipework.

In any case, for a normal sized domestic house every one of these systems
will provide superlative performance. For an extremely large house or small
hotel, more design considerations may be needed to choose the appropriate
system.

Christian.