(Full disclosure: I work for a GM dealer.)
In the sub-$5,000 segment, you're probably best off minimizing your brand loyalty. Take sanddrag's advice and test it well. If you have a trusted mechanic, bring them along; if you're a take-it-to-the-dealer type, most will perform their used-car check for you at the standard rate (figure on $100, but call them first to confirm).
The market right now isn't going to be as rich as it was a few months ago due to the CARS program--regardless of one's views on the program, it means that nearly a half-million cars that were presumably worth less than $5,000* are now no longer on the roads. Even if you didn't want the cars that got scrapped, the folks who did are now going after the remaining cars. This might mean that your best deal is a few months off, but you'll know the local market better. Trust your gut.