I've owned many used cars over the years, and although it can be hit or miss, I personally don't think it's worth the hassle - unless you're a student or really tight on the budget.
I don't believe in owning either... I generally have a philosophy of not buying depreciating assets.
I am a HUGE fan of leasing for several reasons:
1) You get a brand new car every 2-4 years, which is big for me because I get bored easily
2) Cars tend to break down and have problems after that initial 3-4 year period, so you're basically getting the car's best years (while it's on full warranty), and then pawning off the subsequent problems and repairs on someone else
Of course, leasing is slightly more expensive than financing, but I think it's worth every penny.