I don't know about you, but if I was looking for a personal email address, I would go for my surname, rather than my first name. Now that's maybe just my personal preference?
If I were to start a company using my name, then it would be my surname, rather than my first name. I would imagine that to be the case with most? If that is the case with the majority, then not only are you selling a surname to a person, but also a potential company name.
So, personally, I would put more value on a surname, especially one with more people out there!