I'm replacing an aluminum glass sliding door. Should I replace it with another aluminum door or go with vinyl?
Aluminum is heat conductive and sweats in the wintertime as moist, warm inside air hits it. Despite drainage built into the frame, the water also condenses on the outside of the frames and can rot out the wood that forms the rough opening. Foam sealant will help eliminate the air spaces that allow this to happen but doesn't stop any exposed surface from getting damp and dripping. In windows, this leads to black mold growing in the tracks in the winter, no matter how hard you try to keep them clean.
Vinyl is self-insulating and prevents a tremendous quantity of this condensation from happening. Quality sliding doors have a stainless steel cap-strip for the rollers to run on and will outlast the aluminum rib most aluminum doors use for support.
Extra attention must be paid to installation as the vinyl frame needs proper support, a square and flat opening that won't distort the frame, and the door track checked to be properly level and straight. Vinyl is pretty tough, but not rigid like aluminum.
Note: Always use low-expansion foam to insulate the gaps around the frame between it and the rough opening so you don't distort either type of sliding door frame.