Big dog, big bowl
I have a black lab that is 5 months and after thinking the large would be too big for hiking/backpacking with my pup, I've realized that she will outgrow the medium bowl that I bought in a hurry. That said, the construction of the bowl is great and the portability is exactly what I was looking for. I think for car camping or road trips a large bowl would be ideal for any bread that is in the lab or similar size category. For the collie, spaniel size dogs, I'd recommend the medium...or if you're a light and fast hiker that has a four legged hiking companion, the med will be great.