It is up to you to decide which will be better for you. Trade-ins are not often the most profitable route to take, but they are convenient. If you know what you want to do, for example, get the new iPhone or Samsung Galaxy, then a trade-in is a great solution.  If you need more money than you would get offered for a trade-in, selling your old smartphone outright is far better since you can make nearly double the amount of money from a direct sale without third-party involvement.