I've seen a lot of spaniels work, also labs, other gun dogs, a large range of terriers, some hounds and mongrels. . . . .
Whatever you say, you are going to put someones back up, and if I had a pound for everytime someone pointed out that their dog did the job as well (or better) than a purpose bred dog. . . . . I wouldnt be sat on here. . . . i'd be sat in the sun . . . a very rich man!
Both of the breeds that you have mentioned are brilliant for the job in hand, and of course, how they take to it, will have a lot of dependance on how they are bred, brought up and trained etc. You wil