This could be a long thread!
I'm a raw feeder and convinced that it's the best for my dogs. Until I switched William to raw 4 years ago, when he was 5, he was always at the vets with itchy skin, ear infections and lip fold pyoderma. They all stopped when I changed him to raw and have never troubled him since. I'd tried him on various kibbles before then and although his skin was a bit better when he was on Burns than on 4 other previous kibbles it was still far from perfect.
With raw you need to do some research in order to work out a balanced diet, or feed one of the "complete" minces that contain bone. But once you've got the hang of it, and tweaked it a bit to suit your dog (for instance, William has quite a lot less bone than Louis or he becomes constipated) it's easy, fun and most dogs benefit hugely in my opinion.
But I realise that not everyone wants to feed raw. So it's then a case of looking at the ingredients in processed foods (wet or kibble) and deciding what's good and what isn't, or considering a home cooked diet. If you go for home cooked you need to do some research in order to work out a balanced diet, but once you've done that it can work well.
The argument for processed foods is that they contain (or should contain) all the nutrition a dog needs. Unfortunately many of them also contain a lot of unnecessary fillers to bulk the food out and make it cheaper, and there's no getting away from the fact that they are processed and not natural (sorry, raw feeding enthusiasm coming out there). They often include wheat and corn (maize) which many dogs find difficult to digest and some will be sensitive or allergic to. Again, research is needed to find the better quality ones and weed out the rubbish ones.
I saw Countryfile and agree that there was no absolute conclusion, but he made some very good points:
Avoid the multi coloured kibbles as they contain colours and preservatives to make them look attractive to humans (Baker's is a prime example and also has rubbish ingredients)
Avoid kibbles that are bulked out with maize, wheat etc. as they will have low nutritional value and dogs don't generally digest them well. Rubbish and fillers going in = lots of rubbish (large poos) coming out the other end!
Always look at the ingredients before you buy. Look for a named protein source as the main ingredient, such as a named meat or fish, not just something vague like "meat and animal derivatives"
He also said that raw is good but pointed out that you need to know how to feed a balanced diet.
The whichdogfood website is very helpful and has explanations of the minefield that is dog food labelling. But bear in mind that the star ratings are influenced by members of the public making recommendations and companies like Eden have, in my opinion, played that card very well. I'm not saying that Eden is rubbish, just that they've promoted it very well!