Isolate and concentrate is basically the same protein, but the isolate is filtrated more. The upside is that you have a bit more protein (like 1-2g per scoop) and a bit less fat or carbs (1-2g per scoop) which, to me, is insignificant.
However since isolate is basically only protein, it also lost it’s active microfraction content (like lactoferrin) which have immune-system boosting effects.
I used isolate back in the days because I thought that only nutrients were important, but now I don’t. First isolate is way more expensive without actually giving you a lot more protein.