The strict answer to your question is, "Both".
Practically, though, most people who ask me a question like this know very little about computers (which is not a bad thing, it's just a fact). And in turn, they tend to use their computers for word processing and web surfing (not a hardcore gamer -- people who play intensive graphical games).
Here is a hard and fast rule about anybody who meets the above criteria (just a web surfer and a word processor -- not somebody designing an airplane on their computers):
1. Buy the cheapest new computer you can find out there. It really doesn't matter which one. Wait for deals (Dell has deals all the time, check www.bensbargains.net every day for a few weeks). The very cheapest new computer today is more power than you need.
2. Go to www.crucial.com, enter in your computer information, and buy 2x to 4x the amount of RAM that came with the new, cheapest computer. It will always be cheaper than from Best Buy, Dell, etc.
3. Wait for 1 and 2 to arrive; ask a geeky friend of yours to come over and install the RAM. For a geek, it takes 5 minutes. Give him or her a slice of pie as reward.
You will end up with the most cost-effective computer, which will COMPLETELY meet your needs, for the lowest possible cost.