Using a car dealer
When you buy through a car dealer there are legal protections in place for the consumer which gives you a safety net and peace of mind.
Car dealers often have little wiggle room on price so you're less likely to be able to negotiate the deal of the century. Their accessories can be expensive. Unfortunately a small percentage of dealers, despite the legal protections in place for consumers, are as bad as the reputation suggests.
Buying through a private sale
With private sales you can get a really good bargain, and there's often lots of room for negotiation. But there are many pitfalls to be aware of.
Private sales are not bound by the Consumer Guarantee's Act (CGA) and sellers are not required to give a history check (that would alert you to any red flags like the car still having an interested party which has the right to seize the car if the previous owner has not completed payments on it.)