it completely depends on your macronutrional needs. If you need a lot of fat/calories in a meal then eat the yolks, if you just want the protein, or will be getting the fat from another source, then just eat the white. There is no cut and dry answer to "should i eat the yolk or not".
I eat eggs twice a day. I have 1 yolk (plus a lot of whites) with breakfast for the cholesterol, and have a big bowl of oatmeal. Towards the end of the day I switch to no carbs besides veggies and any tag-along carbs (mainly from cottage cheese, which isnt much) and have another serving of eggs with 4 or 5 yolks.