The phones you are looking at (X, 7, 7+) and the other two that can be considered (8, 8+) are so good, that really it comes down to a matter of taste, and also the small practicalities. Do you want FaceID or TouchID? Do you prefer the home button, or can you do without it? Do you prefer the classic iPhone look of the 7s and 8s, or the new Frontier of the X? As far as which one is best, it's really a dead-on tie between them all. Choose the phone you think looks the coolest and the one you think you would be happiest with.