I'm also going to suggest that you start in the 172, for the same reason that you would probably not suggest a student driver to learn in Porsche, even if it was just a 356. I realize that some people will thrive under the additional pressure, and the "more capable" airplane MAY enhance their experience. I still believe that logging some time in a more straight forward plane will be beneficial.
Leigon, I am attaching a picture of a super decathlon (aerobatic pic), a cessna 172 (*boring* tricycle gear), and a cessna 120 (*boring* tail dragger). I think the difference between tail dragger and trike will be obvious. What may not be obvious is that the tail dragger can be more difficult to handle on the ground, and you lose some visibility directly in front of the plane when it is down.
Tim, I have most of my time in a 150, and I have been told it might actually be a little harder to fly than a 172. I'm told the larger plane's mass helps stabalize the flight some, and that the 150 is more hands on. I've never flown a 172 so I can't comment.
As a fellow student pilot I will say that I have some very limited time in a Mooney M20 C, and I really do appreciate the 150 basics. As a reasonably skilled car and motorcycle operator, I was a little surprised to see how easily a novice pilot can begin to feel overwhelmed. I would suggest not trying to run before you can walk, as you may manage to beat all the fun out of it..... Then again, the first guy who did it, had never done it before!