Unless you have a preference for the OS, or already have software designed for one of the OSes, I'd take the Axim X51 low for an extra $24. The reason is power:
* The processor is more than twice as fast.
* It has more than four times the memory.
* It has a larger display, something that will really come in handy when taking notes.

Now, since you're a student I'd also suggest looking into a program that keeps track of all of your classes, assignments, and grades. The top two programs in that category are 4.0 Student ($30) and The Dog te It ($15). Both have free trials, so feel free to give them both a run for their (your) money.

Hope this helps,