There isn't really a correct answer to this, it will depend on what you're looking to photograph, what the weather is like, the seasons and all sorts of other factors. However, if it's a sunny day, the time around sunrise or sunset know as the golden hour, is that best time for photography. After all, photography is all about light, and during these times, the sun is low on the horizon and as was mentioned earlier the blue colours are being scattered more by the atmosphere leaving beautiful warm light. This warm light can make for incredible sunsets, but it's also a fantastic time for photographing other things such as people or animals because of those stunning warm colours. Alternatively, if it's a cloudy or overcast day you might actually be better off in the afternoon as it will get darker sooner and during the daytime, you won't have to worry about harsh shadows on people's faces caused by a high sun. You won't get the best warm colours, so you may want to consider shooting a more vibrant colourful scene such as in a forest, shooting up close (macro) or even shooting a waterfall/ river (there's a whole other blog in how to shoot them!)