I don't know where you are located but sliding windows by design are the least efficient windows on the market due to the amount of moving sash members. I although don't personally like vinyl windows I would go for the Simonton as Weathershield product's(especially vinyl) can be suspect. Unless you live in a warm climate or are on a tight budget you would be better off looking into casements or casement/picture combinations

After some additional research we found that out. We have decided to go with Casement & Awning windows.