The "if I could have only one powder" scenario is not valid these days IMO. There are so many companies with many powders available we don't need to make that choice. We are truly lucky to have all these choices.
I do use 3 or 4 handgun powders most times but I do have a dozen on my shelf. I sometimes use a powder for only one application like AA#5 for Speer 135gr .38 Special +P replica loads.
As an addition to my first post I will add the other powders I have and sometimes use. (most are on my shelf right now)
Clays, Universal, W231/HP-38, HS-6, Longshot, W296/H110, Lil'Gun, W572, AA#5, AA#9, Bullseye, Power Pistol, 2400 and Trail Boss.
H4895, IMR4895, H4350, IMR4350, Varget, IMR4064, IMR3031, LVR, H4198, IMR4198, H335, BL-C(2), IMR4451, AA5744 and TAC.
Sometimes if I have the Hodgdon version of a powder on the shelf I won't buy the IMR version and with W231/HP-38 and W296/H110 I buy the one that costs less at the time. I didn't list powders that I bought one or two pounds of and never replaced when empty. Powders like ZIP which I bought during the shortage that is very similar to W231 was not replaced or listed. I have 12 handgun powders on the shelf right now and 11 rifle powders.
Some reloaders like to load with as few powders as possible, I'm not one of them. Using many powders allows you to load during shortages with many different powders and data you already worked up and tested.