What is a better foundation, concrete block or poured?

I did not realize that anyone could 'dry stack' concrete block, untill after reading this thread.

I was taught to mortar the blocks together [which gives space to lay the horizonal rebar] and then to fill the voids and vibrate the mortar down into them.

This is what I am doing for our 'lap-pool' that takes up the Eastern end of our new home. A 40 foot long 8 foot wide pool for swimming laps, just off the master-bedroom.