I scrap at 12x12 so that I have options but I prefer to print at 8x8. I have a few 12x12 photo books and I have duplicates of those same books in 8x8 and I prefer the 8x8 in almost every case. The size is just so much more convenient. I don't find that my journaling is too small to read or pictures too small to see or anything like that. I like the 12x12's but they are just so massive that no one bothers to get them out, ever. The 8x8's are out all the time. I have probably 40 8x8 books and my kids carry them to school with them, take them to friend's houses, sleep with them in their beds, etc. LOL They are, IMO, the perfect size.
My books are all Shutterfly too. I haven't tried any other company yet because I've gotten every one of my Shutterfly albums free (most with free shipping as well) so I haven't had a need to buy any yet. I also have triplicates of each of the 40 some books. Two of each are put up. When the kids grow up they will get a copy of each and we'll have a copy of each left.