I have printed up to 16x20 but only a few times, and that was to print something I sold. Usually 8x10 or smaller depeding on format or cropping etc. Sometimes 11x14, but mostly contact prints in that size.
I have always found that it is really a moving target. I may think big is great and then go to a gallery or someone's home and see a bunch of 4x5s or something about 5x7 in large mats and frames that really look great. I am getting to the opinion that where the print is to be displayed is the deciding factor.