I tend to use either Ultra or Final. Ultra when It's not too complex, and I know it won't be an all day thing, and Final for those other times. One thing you can do to sort of fake it is to render in Final mode much larger than you plan on needing, and then after it's done, scale it down in an image processing program and maybe add a slight (very slight) blur. You need to use Ultra or better, I think, if you want to use more advanced features like motion blur and soft shadows.