I have always used Ubuntu, and never thought of using Debian till I had to take Google Compute Engine for a spin, and the only image that they had were Debian images (at that time ... now they have Ubuntu images as well). So I used a Debian image and found myself quite at home. I suggest you go with Ubuntu if you are relatively new to Linux, as there is generally more support and material out there to help you. If you want better flexibility, maybe Debian is better, but I cannot vouch for that. Either way, you can't go too wrong.
But I am assuming you are running a server, not the GUI desktop. If, on the other hand, you are looking for an appropriate OS for your laptop, there's no doubt in my mind that Ubuntu is better.