Our web app is running in .Net Framework 4.0. The UI calls controller methods through ajax calls.
We need to consume REST service from our vendor. I am evaluating
Firstly, I am not an authority on WebClient vs. HttpClient, specifically. Secondly, from your comments above, it seems to suggest that WebClient is Sync ONLY whereas HttpClient is both.
I did a quick performance test to find how WebClient (Sync calls), HttpClient (Sync and Async) perform. and here are the results.
I see that as a huge difference when thinking for future, i.e. long running processes, responsive GUI, etc. (add to the benefit you suggest by framework 4.5 - which in my actual experience is hugely faster on IIS)