Ratings are what you go by, if im wrong ok but by the design of pulling
a window into the frame as casements do my limited research of air
infiltration ratings showed casements superior, in air infiltration. I
know my casements are still tight after years, and my sliding glass
doors, Anderson a bit loose now from constant opening. It is logical a
sliding seal will loose efectivness faster than one pulled tight. One
other rating of many of importance is CDF, condensing factor, my Pellas
condense, my Andersons dont, I researched this to late as Pella at a
Consumer Reports test article, is rated lower on Dual pane Low E argon
than Anderson. For windows depending on where you live there are
different types of E coatings, some optimise SHG for high heat areas
some reduce SHG, solar heat gain. Windows have alot of science behind
them to save energy. Hurd offers several types , good to look at what
they offer to see what is location important, they have high SHG and
lower SHG types. In Fla you want low SHG and VLT in Minnesota for
example you would want high SHG + VLT. There is always something new out
with glass to make utilities less of a burden, glass is not equal as
salesmen tell you. Google there is alot to read.