With CSJ there is quite a variety in the quality of the ingredients in the various products. Some of their dearer ones are ok eg Command Performance), but the cheaper ones (CSJ Original and Champ ranges tend to have wheat as the second largest ingredient - in one case it's even the largest ingredient, and the meat content in them tends to be "meal").
If cost is a factor, then I'd say that Pets At Home's own brand, Wainwrights, is a better quality than CSJ.
I wouldn't say either are the same high quality though as Arden Grange, Barking Heads or others which use human-grade meat. I personally feel that Arden Grange is well worth the extra money.