I have a large Arkel bag, my grilfriend has a small. I have a DSLR with two lenses, plus a lot of other stuff that goes in my bag. The large is huge and perfect for me, it isn't waterproof though (you may want to get the rain cover). The large has a few more features (more pockets) which is nice for me (I love to organize things). The small is nice as well, because it is small, my girlfriend usually carries the sunscreen, guide book, tp, wallet and a few other things, so there is enough room in the small as long as you don't have a massive camera. I would definitely recommend the Arkel bags, there was a lot of though put into the bags and when I am on a plane that bag is my carry on, carrying everything I need.