ASP.NET WebApi会话与静态变量

这两个存储全局变量有什么区别？

private static Dictionary<string,string> ConnectionStrings
    {
        get
        {
            if (HttpContext.Current.Session["ConnectionStrings"] == null)
                HttpContext.Current.Session["ConnectionStrings"] = new Dictionary<string,string>();

            return HttpContext.Current.Session["ConnectionStrings"] as Dictionary<string,string>;
        }
    }

和

private static Dictionary<string,string> connectionStrings = new Dictionary<string,string>();

我应该使用会话或静态变量来存储动态生成的连接字符串(长篇故事)吗？