Not an expert, either, but I trust any of the pet store brands, because they either have done the research or formulate according to the research (I forget the name of that large animal nutrition research center in the UK). I fed Friskies (which is probably one of the best grocery store foods - and I would still recommend it for people who cannot afford or choose for other reasons not to feed pet store foods) for years and always had FUS, tooth, and skin/coat problems. Then I started feeding Hills after k/d was prescribed for a kidney patient and I first read about the above mentioned nutrition research center. All nutrition related health problems ceased. Since Iams has come to the grocery store I've started using it, and like it even better than Hill's (although "best" can vary from cat to cat so this is certainly no indictment of the quality of Hill's). My cats are very active and healthy with very glossy coats (even the cat that doesn't have the "glossy" type fur), good skin and strong, clean teeth. One is overweight but he got that way on mother's milk, so I attribute it to his genes. I find it is in the long run no more expensive than Friskies, first of all because a smaller amount fills them up faster, also because there is less waste in the litter box so less litter needs to be purchased, and I have fewer vet bills. I buy the eight lb bag for about $13 and it feeds four cats for two weeks. I occasionally will give treats of cooked meat because I feel nothing in moderation will do any harm.

A good website for any pet concerns is Iam's: http://www.iams.com
but of course, they could be accused of being biased since they do sell pet food.