When you want to design/test your caml query, most of the time uses U2U CAML Query builder. Sometimes you get problem with connection but most of the time, it was working fine for most of the needs.
Recently, I tried CAML Designer which is
really nice tool to try as alternative. WPF UI experience with many additional
features may impress you to switch to this new tool.
Let me know your
experience while evaluating