Neither. The ideal situation would be a mix of both sun and shade. The sun in the morning hours, shade in the late part of the day. We know this isn't always possible, but a good rule of thumb if possible. To much shade may have less algae, but it will be tough to have plants. To much sun means more algae, but great looking plants. Keeping a 70% plant coverage will help.

If your pond will get a majority of late afternoon sun, figure on using a UV and a larger filter system so that you are sure you will be covered.