I personally prefer standard length (35mm) cartos and tanks. I think shorter tanks look better, and they give a slightly shorter overall length for your setup. With standard length tanks you can also use any cartos you want, as 45mm XL cartos will fit fine in a 35mm tank, just stick out a bit. It doesn't work the other way around, as you can't use a 35mm carto in a 45mm tank without some sort of extension or adapter.
XL cartos also have a bit more length for the vapor to travel before getting to you, which could potentially cause a cooler vape but it's probably so miniscule as to be undetectable.
So it's just personal preference, there really isn't any performance difference between the different sizes. ST's super shorty cartos do have a much warmer and flavorful vape though due to how close the coil is to your mouth. I can't wait until IBTanked gets their shorty tank tubes online.