INTP
I've done this test before in many places (including an official one administered by a psychologist), and INTP is what I tend to get. I do prefer this site for the description, though the one on the OP's linked website is good as well.
The only problem I have is that I'm not sure if my answers to the test are who I am, or who I wish I was.
...Which seems to fit the personality type, really.