While the suggestion is from most of the manufacturers that Isolate or Hydrolyzed Whey Peptides are better, in fact, this is commonly an acid process which destroys the bonus factors of the whey protein. Hydrolyzation is a "pre-digestion" process which makes the protein enter the muscles quicker, which is good (most likely, although this also depends on your purposes for eating the protein at that moment), but the other major components of the whey protein, called sub-fractions, are damaged in the process. To our thinking, this is the main factor against most whey protein isolates, which are usually acid processed.
STICK WITH PLAIN WHEY PROTEIN CONCENTRATE. Results wise, it is often better than Isolates or Hydrolysates and yet it costs virtually nothing!