IMO Aptamil and Cow & Gate are virtually identical, and equally good. I've read in a few places that they are made by the same people in the same factory, and having used both I could not tell any difference. The only difference I know of is that C&G is cheaper!
The only one to avoid is SMA, no end of people seem to have problems with it, compared to hardly anyone with the others. Don't get Heinz Nurture either, as it's discontinued.