For me, it depends on outside temp. The main advantage of AC is dehumidification. So if it's 95 degrees and humid outside, 78 degrees inside feels great, and keeps the AC running often enough to keep humidity down.

If it's in the 80s outside, I'll probably drop the inside temp to 76, again to keep humidity down. I rarely set it below that. 74 feels cold in my normal summer attire of shorts and a tee shirt. If we have an 80 degree day with low humidity, I'll open the windows.