I'd argue that salt, CL or TA would be a bit better for estimating use. pH and CYA depend on subjective estimates of perception changes (what color is that?, did the dot disappear there?)
The three drop tests are better when starting from high levels (more drops to make a change). But none are all that precise to allow a one time calculation. Best to sneak up on it. For mine, I assumed it was roughly 25K gal to start. Added what Pool Math said to to get the result. Oops, result was a bit low. Changed pool amount to 20K, now result was too high. Ending at using 23K gets me close enough for all future additions.
As noted, CL gives the fastest cycle time, is subject to environmental swings, but is self correcting if you go a bit over (given time for it to come back down). Salt is hard to bring back down, and TA gets messy trying to chase with soda and acid.....