I also print mine 8x8. I have one album I did as 12x12 and the pages just seem gigantic to me!
So, I prefer 8x8. I've ordered prints from scrapbookpictures.com and they were great. Normally I order from sbtoshare.com because I love their cardstock paper.
ETA: They charge $1.50 per page for 8 1/2 x 11 prints. The only downside is they print your 8x8 on 8 1/2 x 11 and then you have to trim it yourself. I don't mind doing it but it's one extra step if you want that size from them. Anything larger is $2.00 per page.