Consumer Reports recommends what Clint already posted: get a savings account for repairs and take what you would spend for the warranty and place it into the account. By the time the factory warranty runs out, you should have a descent amount in the account which should cover most repairs. You just have to remember to makes those deposits or, better yet, have them direct deposited from your paycheck.
For a year, I left Nissan and worked as an independent mechanical inspector for various extended warranty companies; it was my job to go to the repair shop where a claim was being submitted and take pictures and assess a cause for the failure and report it to the insurance company, who would make the determination if the claim was covered or not. There are a lot of warranty companies out there outside of the vehicle manufacturers and some are good and some are terrible.You need to make sure you read the fine print of the warranty coverage and know what's covered and what's not. Many plans don't cover seals or damage caused by failed seals, which is a large percentage of the failures that occur; it usually eliminates most automatic transmission failures outside of a hard part failure, which seldom occurs by itself. It also eliminates most turbo and hydraulic system failures, like brake master cylinders and calipers or power steering pumps and gears.
There are also different plans. When I was a tech, Nissan's warranty had a gold plan, gold plus, silver plan, etc. There were different deductibles and some covered a rental vehicle and some didn't. If you put a lot of miles on a vehicle, they usually don't pay off as most don't cover more than 100,000 miles, which most vehicles can last without a lot of major problems these days. As said, it's a gamble either way. One more thing... If you do get a warranty, make sure you keep up on your services and keep all receipts for the work done!