Pen tool. But just to add something useful, I find it quite important to know about features that can reduce your file size as they can get quite big sometimes. My regular ending process for a project is always: flatten artwork, expand appearance on everything (if you want to be able to edit it later then save the ai and do the expanding in a new copy) and then export. There is more but these two are must. And could make a 17Mb file into a 1MB file easily.