To the original poster - what makes the most sense to you? What do you think will get your soup safely from the pot to the blender? Of course a ladle will - ANYTHING that you can dip in the soup and pour in the blender will do the trick. I use a coffee mug or a measuring cup. You want to be sure that at the end you still have some liquid to solids to blend together and not just all solids. Just use a little common sense. At the very end, if the pot is not too big, I may pour/scrape the last bit directly into the blender.
It probably would have been nice to know what kind of soup you made i.e., was it very chunky? You don't want the chunks to fall in the blender and splash. Solids can shift fairly quickly causing a MUCH bigger mess and thus not being so efficient in the end i.e., all that cooking and nothing but a few cups to show for it!
You also don't want to fill the blender much past the half way mark with a hot liquid. It will build up pressure and when you remove the lid it may splatter out causing a burn - or at least something uncomfortable and messy.
In the professional kitchen I worked in if we made a soup that required additional processing in a blender or food processor we ALWAYS used a larger measuring cup or a larger ladle - we NEVER poured directly into the blender/processor. #1, the pan we cooked in was usually pretty large and wouldn't even make sense to pour directly into one of these appliances (once you push the limit and solids start to shift you're pretty much screwed) and #2, the most important thing, it just wasn't a safe practice for several reasons i.e., burns and well, spillage, which equates to food costs and a HUGE waste of time when you don't have a soup for dinner because it's on the floor.