If Sam's good on the food he's on now, I personally would stick with it
What suits one dog, won't suit another. Jess can't tolerate kibble of any sorts (she has a super sensitive tummy), so the only option for me was raw (I don't believe in tinned meat for my dogs), and I've never looked back.
I would recommend raw as a food, but I know not everyone likes the idea (it took me a LOT of convincing for me to consider it too).
There are loads of kibbles that are good. A friend of mine has her GSD on WAGG and he thrives on it, but yet that's a food I wouldn't touch with a barge pole, so as I said earlier, what suits one dog won't necessarily suit another. It's just finding one that agrees with you and Sam.