Don't mean to be rude, but you should try and do a little research. I recomend buying a car that you overall like. I know this sounds obvious but many people don't think about these basic things when buying a new or used car:
Whats my budget?
Coupe, sedan, hatchback?
Drivetrain...FWD, RWD, AWD?
Reliability...What years are you limiting yourself to?
Just my thoughts on the matter. I suggest honing in on what you want or think you want. If you still can not decide after honing in on a specific type, come back to the forum and ask a question like so...
"Whats the fastest/best 02-06 sedan with AWD for around 18K?"
Hope I was helpful.