I had a Blowfish. It was a little too big for daytime riding. I've had 2 Mules since and love them. 100 oz of water and room for tools, tubes, food and a jacket. When I start an afternoon ride I can carry my lights in there if I don't want to put it on my helmet until dark.

On the other hand, if I'm just doing a short ride, i don't have to carry much at all except up to 100 oz of water. I rarely ride off road without my pack. It just feels wrong now!