In my opinion, it's just a matter of preference. I don't think it matters either way. Personally, I like to see the first and last name spelled out without the middle initial.
Unless of course blah.com is actually an email address at one of the big outfits and you have to include your middle name in order to acquire an account as all the the other names are taken?
In my first post I was assuming that blah.com was your own domain name.
If it is, and you're just asking for opinions on what to use before the @blah.com, I would personally go with jdoe@blah.com. I wouldn't include my middle name or initial at all.
That's assuming j is the first initial in your first name and doe is your last name.