Sorry o hear sam is poorly but at least now you know he wasnt being naughty or forgetting himself.
As for feeding it really is a matter of personal choice. My preference is for a dry complete food although my breeder is against them.
I prefer them for the convience and they fact there is usually less "waste" coming out the other end and what there is is firm and easy picked up. Also dry food is great at keeping teeth and gums healthy - all that crunching
Tinned food is around 70% water so stools are going to be looser and you need to add a mixer to help the teeth
As to what brand, i would say go for the best quality you can afford. Atm I changing Alfie over from JWB (which is a very good food) to Burns (also a very good food). My reasons are that Burns, from others postings, seem to keep the weight down on the dog. This is something Im concerened about as I had a big battle on my hands keeping the weight of my last cocker.