vector art yes... Illustrator would be the choice but for speed you would need to know when to use the pen, pathfinders, brushes, blob brushes, custom lines, the hand tools... and goes on.
after you get used to illustrator you should be able to work at high speeds, its recommended to sketch on paper or another sketching program before, illus really sucks for sketching.
Another HUGE advantage of Illustrator is the creation of one object and then being able to just modify it freely to create another with little to no work, take the guys holding Tiana in the last pic (Heck yeah that movie was awesome xD) you can see that they're all the same, you create one and then rotate it, then add two in the back, shrink them a bit and change their skin color with just a click. Gotta love Illustrator :P
Hope that helps Lego.