Back when I was teaching a Satureday computer class (in my spare time), I was asked this question frequently. Unfortunately, the answer is very vague: "It depends."
It depends on what you want to do with your computer. Do you need high-end graphics in order to play Second Life or Video Games? Do you simply want to connect to the internet to do email and surf? If you all you want to do is surf and all you have is a dialup connection then you won't need a big fancy computer becuase you will have an extremely slow connection which will act a a bottleneck and the speed and "fancy-ness" of you computer won't matter in that case.
Are you wanting to read and write to the disk alot? Well then you willwant a system with faster disk speeds. (because then I/O is your bottleneck.)
I guess it all comes down to this: What do you anticipate your "bottlenecks" to be? Dial up? Memory? I/O? Graphics?
Generally the system that you will pull off the shelf at the sale price is going to be barely enough to run certain kinds of programs. In this case - you did not buy a "bad" system - it may run slower than you expect because you are putting demands on it that it isn't built to do in it's "off the shelf" configuration. Often times, simply adding another gig of memory (get it up to 2gigs) and going for the faster DVD drive are two things that may make your experiences much better - regardless of which system you choose. Personally, with everything I like to do on my PC at one time, I am enjoying the Core 2 Duo technology - it is much more power efficient and having two CPUS is really nice. But again, it depends on what you want to do with it (and for how long.)
You should also find online reviews of both systems that you are considering and then make an informed decision.
I hope this helps!