WebClient vs HttpClient

Web­Client	Http­Client
Avail­able in older ver­sion of .NET	.NET 4.5 only. Cre­ated to sup­port the grow­ing need of the Web API REST calls
WinRT appli­ca­tions can­not use WebClient	Http­Client can be used with WinRT
Pro­vides progress report­ing for downloads.	No progress report­ing for downloads.
Does not reuse resolved DNS, configured-cookies.	Can resuse resolved DNS, cookie con­fig­u­ra­tion and other authentication.
You need to new up a Web­Client to make con­cur­rent request.	Sin­gle Http­Client can make con­cur­rent requests.
Thin layer over WebRe­quest and WebResponse	Thin layer over Http­We­bRe­quest and HttpWebResponse
Mock­ing and test­ing Web­Client is difficult	Mock­ing and test­ing Http­Client is easy
Sup­ports FTP.	No sup­port for FTP.
Both syn­chro­nous and Asyn­chro­nous meth­ods are avail­able for IO bound requests.	All IO bound meth­ods in HTTP­Client are asynchronous.

原文地址：http://blogs.k10world.com/technology/webclient-httpclient-consume-http-requests/