I want to rework the water supply pipes under my kitchen sink, and I want
the result to be very modular, in the sense that I can disconnect something
and connect something else, without doing any plumbing work.

For example, if I decide at some point in the future to add or replace a
valve, I want to be able to unscrew flexible pipes from the old valve and
screw them to the new valve, such that the whole job of replacing the valve
would be just a few minutes.

What kind of connections are best and most reliable, for that kind of
modularity?