Depending on what thermometer I use, anywhere from 74F-80F. I should invest in an accurate one someday.
Taking temperature by committee, AKA using a few and seeing which result is most common, mine are 75F-78F. I keep my fishroom sealed up as best I can and run heaters in the lower tanks and any tank with special temperature requirements. Those combined with occasional heat from the dehumidifier and whatever heat is realized from the furnace vent keeps all of the tanks at least at 75F, if not higher.
I do think that I get slightly slower fry growth rates from the cooler temperature tanks. This is based on comparison of tanks sitting side by side, one with a heater (~78F), one without (~76F), and fry in both from the same batch. I'm not trying to make money breeding, it's only a slight difference, and I haven't seen any health side effects, so I'm not too concerned about it.