Hi,
Concentrates can be mixture of many types of protein, (fast or slow absorbing) whereas isolates are 'supposedly' pure isolate and it’s said to be faster absorbing.
'Hydrolyzed whey isolates' generally speaking cost more than whey concentrates and manufacturers claim it's supposed to be faster absorbing. I am not yet convinced of that.
The idea behind the hydrolyzed whey isolate is that it should be taken in and around workouts (as its faster absorbing) and of course to take the concentrates the rest of the time (cause it’s released into the bloodstream slower etc.)
I would go for a type of whey that best suits your goals. Low carb whey vs. a high carb whey protein might matter more to you (if you are cutting) than whether or not a whey isolate can be absorbed 10 sec faster than a whey concentrate can. Also some whey proteins have much more protein per scoop, than others. Also go for whey that tastes great, or you may gag.
Generally speaking, protein is protein despite manufacturers’ claims.
I agree with what Bryan wrote. That it's more about the quantity of protein than it is about quality. If you are not consuming enough protein each day, then may be an isolate would be a better choice over the concentrate.