Single slider windows or double hung windows? Which one do you think is the best for homes in any condition?

Checking the specs for air leakage might give a hint. I suspect the sliders will leak more.

Double hungs will probably have slightly lower air infiltration numbers but I bet you could upgrade the sliders to triple pane and still be at a lower price. Then take that savings and invest in energy efficiency improvements where it really counts like the attic or basement.

Sliders will also probably meet egress whereas double hungs likely won’t.

I’d go with triple pane sliders. See if you can put 2 locks on it instead of one which should make a slight improvement in air infiltration.