Both will work if the windows are well built.

I prefer twin double hungs for air tightness but the 2-Lite will have more glass.

Make sure you get a good installer if you go the slider method. They are often times not fully supported under the sill, which leads to sagging and poor operation.

Twin unit for me - stronger and tighter. Sliders that large can be problematic.

I just finish one house with two double hung Simonton windows and whole project look great, Only you have to pay for two double hung windows instead one slider. Price is higher