I love using assorted fruits for a quick smoothie. Making smoothie is just the easiest recipe you can think of because, once you've popped in all the fruits and yogurt and any other ingredients of choice into the blender, the task is as good as accomplished. All of the work will be done for you by the blender, all you need to do is add all the ingredients with whatever additional flavours you desire. Vanilla flavour is always the best option for me but others are still perfectly ok.
But trust me, any flavour will really work. If you want anything lighter, you can add a little more milk if you are using vanilla cream otherwise if its just fruit, then add only water or even ice cubes. Just go for what you like! Then for the fruits, you can choose whatever fruit you have on hand and each of them add different and special taste to the smoothie but, whichever one is just brilliant.