The 3 I have: (this is for standard 53-39 front end)
12-23 for flat to rolling
12-25 general purpose, good for almost anything
12-27 hilly courses only
I also own an 11-23 (came w/ the bike), but since I never actually need the 11, the 12-23 gives me one more gear where it’s actually useful, vs one I pretty much never ever actually use. If you are going above 33-35 mph, you aughta be coasting and aero anyway, so why pedal?