Which time of the day that is best to take pictures?

Lighting is one of the very important elements of taking a photograph. It really depends on the affect, mood etc. that you want with your image. It also depends on the subject matter and content of the image. Any light can work if it is the right light and works with that image. However, side lighting such as early mornings and evening lighting help bring out the texture and color much better than midday lighting in most cases. Side lighting like this also tends to be more dramatic. Midday sun tends to wash out more images than the other too. Do you want a silhouette then you need a back lighting. Working with existing light can be fun and works well with nature and natural shots many times. There are a millions answers to the question but it really boils down to paying attention to the lighting and how it really looks on your subject and what you want the final image to look like.