Do you guys do deadlifts on leg day or back day and why?
Back day! I like to keep my motion ranges together. Whether it's push or pull day, in the case of deadlifting. If I am shooting for a max, I will let it have it's own day with some added extra movements after.
You could do them on either because of the overlap in hamstrings/posterior chain. Just make sure you accompany the load, volume, and bodyparts you are targeting properly. You do not want to overstimulate a muscle or not allow it to recover properly.
I've been doing mine on leg day! Especially if I do legs twice a week I'll have a day with squats and one with deadlifts. It activates a lot more of hamstrings/glutes for me personally (obviously with everything else thrown in there).
Regular Deads on Back Day
Stiff Leg Deadlifts on Leg day
Rack Deadlifts on back day
Stiff leg deadlifts on Leg day
a good way to break up the deadflit into two days without overlapping body parts.
Back day, simply because Deadlifts are extremely exhausting and demanding. To pair that with back squats would not be fun. I do front squat after deadlifts though.