I voted one, for one at a time. Which one that is varies however. D76 when I was learning, or when I've shared a darkroom and that was what the darkroom stocked (I like it fine, but don't want to deal with powders at home). HC-110 dilutions E or H at home for some years, then Tetenal Ultrafin (worked well, went off too soon, but had the courtesy to turn a funny colour before dying), and Mörsch EFD for the last year or so.