Just to show off my work:
my fluid logic "input selector":
at heart, it's nothing but a three-way input inflow with enable gates for each input, and a "reset" switch so the whole thing can be put back in neutral if wanted:
##~...
##A##.
##X##.
#R^YB~
##Z##.
##C##.
##~...
A, B, C - doors operated by the three data inputs
X, Y, Z - doors operated by the equivalent "enable" signals (X enables A etc.)
R - Reset door, allows resetting liquid in the cell to low if desired
Yes, it needs fluid from three sides. Hey, it's just water, we got a river full of the stuff.
Opening one of the enable doors makes the cell take on the equivalent water level of the data input (input open - high fluid, input closed - low fluid), regardless of previous state. Resetting the cell between reads is possible, but not required. If desired, multiple inputs can be enabled simultaneously - that outputs the logic OR of the data inputs. Working with doors, it reacts pretty quickly to signals, but as "drainless" design requires a robust water supply.
It takes rather spread-out feed channels, and this internally compact design is restricted to three inputs with and four without reset capability. Still, if you don't really _need_ more out of it, it's quick, reliable and looks nice.