What is the best ?

Diluted white vinegar works amazingly. Cuts grime with a streak free shine.

Since you’ve probably used commercial window cleaners for a long time it will take a few applications, but this is what my company uses. For the first application or for very grimy windows add 2-4 drops of liquid soap (like dawn or Castile soap but not a detergent) to a 32oz bottle of hydrogen peroxide (keep it in the dark brown or tan bottle it comes in). Replace the top with a spray nozzle and use straight from the bottle. For maintaining clean windows, mirrors or any glass surface, use straight hydrogen peroxide. It’s also important to use a clean, dry, cotton cloth, we prefer “flour sack” towels which are lint free, but old T-shirt’s work well too. Never use terrycloth or stretchy fabric like Lycra or nylon. In a weekly basis, just buff the glass with a dry towel, no spray needed

Vinegar and a real newspaper! The ink has lead trace that makes your windows crystal clear.

If you want an over the counter.... I suggest method glass +surface naturally derived glass cleaner. Works great and smells good too.

Personally I mix white vinegar with warm water in a spray bottle using a dust free cotton rag to clean the windows. (1 part vinegar to 3 parts warm water) Best of luck.

Sprayway. Leaves windows, mirrors and glass doors immaculate.