Kongs are very temporary, and only if stuffed with peanut butter/cheese/treats whatever. But you almost have to pack enough treat in to replace an entire meal in order to keep their interest.
My dogs love Biljac liver treats, and I've never seen a problem with diarrhea. But then, they only get two or three at a time during training or nail clipping.
I also use CarryOuts, but for bedtime or when I am leaving the house. Gypsy gets a couple of whole ones, and Jazzy and Keoki get a few pieces. I haven't noticed that they are particularly smelly though.
Nylabones do nothing for any of my dogs. Can't even get them to care beyond the first sniff. I have yet to find a rubber-type bone/toy that any of them will show the remotest interest in.
I want to get a Buster Cube, but I'll need three of them as the dogs fight whenever there's any remote possibility of one getting any more food than the others. So, I'll hold off on that.
Dried chicken liver excites them and is great for training. I buy that from my vet. And it doesn't smell bad.