Wherever possible buy outright, it is always cheaper. If needed, get a 0% interest credit card and use that to buy it outright. Do not fall into their trap of paying hundreds more for convenience and interest, all while never actually owning the device.
For me, it's using emulation. I'm currently playing Paper Mario: The Thousand Year Door from the GameCube, and there are very few android games that can match the quality of older AAA titles.