Compare regions by executable sell-side depth instead of just top-of-book price. Enter the quantity you need,
then see which market can actually fill it, what blended cost you will pay, and where the ladder starts getting ugly.
Start with an item and a quantity. A good first test is Tritanium with a target like 50,000,000 to see why a tiny cheap order in one region may be less useful than a deeper, slightly more expensive ladder somewhere else.