There has to be an historical angle to this (showing my age) for the curriculums in school. Functional was all I had to learn when I started.
But putting that aside, you have to start somewhere so one of them has to be first. If you start with imperative then there will be things you reach for that wont be there when you learn functional and you'll have to get used to doing things differently. If you start with functional and move onto imperative then you'll have to get used to learning new concepts/constructs and remembering that they are there it use.
Whenever you are programming you are trying to solve a problem. It is good to have both in your toolbox to reach for to solve the problem at hand. That's why I think it would be best to start with imerative and then learn functional: if you find yourself reaching for something not there that's indicative of having chosen the wrong tool to solve your problem.
Other than that methinks it's a toss up.
