Best way to use HttpClient, as singleton or new instance for each http request?

Hello everyone,

what is the best practice to use HttpClient?
Is it better use it as singleton or as a new instance for each request?

I'd tried to use it as singleton and it works nice, but when I make two 2 different and consecutive requests (I mean 2 request versus 2 different services paths) the second one return "bad request 400". The problem disappears when I use a breakpoint in Xamarin Studio for few seconds.

Does HttpClient store some value into the Header or something else?

In the code below there is the singleton initialization:

`

        client = new HttpClient (clientHandler);
        //client.Timeout = new TimeSpan(20000);     
        client.BaseAddress = new Uri(ServicesPath.BASE_URL);

        var usernamePassword ="foo" + ":" + "bar";
        var bytes = Encoding.UTF8.GetBytes(usernamePassword);
        var auth = Convert.ToBase64String(bytes);

        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", auth);
        client.DefaultRequestHeaders.Accept.Add(MediaTypeWithQualityHeaderValue.Parse("application/json; charset=UTF-8 "));`

Thank you,
Mario