Comparing 4x6 vs 5x7 shows that the 5x7 will create a larger area for viewing a photograph and make it feel more prominent. More space is also helpful as Visuals Clipping indicates, for portraits and images with significant fine detail, or for family photos. When space restrictions are a concern, a 4x6 print is a good choice. Both sizes are frameable but 5x7 will give it more impact when it's going to stand on its own.