It depends on what you are going to be using the laptop for. For instance if you are planning on doing minor video editing, both laptops will work but the aluminum one will work a bit better. If you are planning on playing SOME games then get the aluminum. If you are planning on doing lots of video editing and playing lots of games then get the pro. For uses such as web browsing, email, word processing, youtube, photo editing, and such, then both machines will work great, and therefore I'll get the plastic one. About the heat issue, the 4th generation macbook uses the same processor as the new one (penryn) and while it may get a bit warm (all of them do anyways), it is not an issue (at least for me). Right know I have been using safai, itunes, microsoft word, and powerpoint for more than an hour and it is sitting comfortably on my lap. After all is done and said, the decision is yours. However, you should at least consider the plastic macbook, and if you can get the black one even better since is not as susceptible to cracking.