VERY hard choice.
1a - G30S, G20
1b - G30S, Gen 4 G17
1c - G30S, Gen 4 G21
1d - G19, Gen 4 G17
1e - G19, Gen 4 G21
Seeing as I don't have a Gen 4 G19, yet..., I'd choose my Gen 3 G19 over my Gen 2 only because of the history I have with it.
The two Glocks I regularly shoot now are the ones I would answer the OP's question with. A G41 (Gen 4 of course) and the Gen 4 G30S I just built from a 36 barrel and slide onto my G4 G30's frame. It is my everyday carry but it and the G41 both go the the range when I shoot.
There are several Gen 2 G19s around the house but they are primarily my wife's guns so she can keep two of them unless she ever gets to see a G43 and likes it. Then one of the G19s will probably go and I'll buy her the 43.
26 and 21. Of course if I reduced down to just those two I would keep the longslide for the 21 and the 27 conversion kit - an upper, trigger housing w/40 ejector and mags - for max versatility.
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