I would use whatever size works. Generally I would upload them into (for me) iPhoto and then crop and size then depending on each individual photo. And I guess it might depend on the photo app you use, or just the camera one. I love Photo HDR fro the filters and it has a square frame, for example.

Not very helpful, I guess but hard to be too helpful with so little info - how will you print? Photobox/Online? at a shop? at home? How will you do the album> print and make lie a scrapbook? and online photobook process? Are the photos all one way - like all rectangular, or some instagram style squares? Do you want to use them exactly as he took them or crop them to fit??

??

LOTS of variables...