"The question is, which is easier; renewing a current passport and then going back to get my name changed on it a few months later, or waiting until after I've changed over to my new last name and renewing an expired one."
A passport can be renewed by mail if the following are true:
1. The passport was issued after your 16th birthday.
2. It is undamaged.
3. Was issued within the past 15 years.
4. New passport in your current name or you can legally document a name change. That means you can submit a certified copy of your marriage certificate.
Passport issued to adults (16 years and older) are good for 10 years, so that means that a passport can be expired for up to 5 years and still be renewed by mail.
If you don't have any plans for international travel in the near future, I'd suggest you wait and renew it after you get married and have your certified copy of your marriage certificate. That way you can do the name change and renewal at the same time.
"Does anyone know how long it will really take to get one in Alabama, it says 4-6 weeks, but I don't wanna cut it too close. Any personal experiences here?"
It so happens that I have some friends who recently got their passports renewed. It took them six weeks. I work for a company that requires, as a condition of employment, that everyone have a passport. Six weeks is about standard for an uncomplicated application.
Your location (Alabama, etc) does not matter, as passports are sent to a national center for processing.
We are entering the "rush" season as people start planning their summer travel. If you are concerned about getting a passport for summer travel, I'd suggest you start now.
If you are planning to get married and change your name, they give you a break. If you apply for a new passport, in your maiden name, then send in for a name change within the first year, they don't charge you the new application fee. If you change your name after you have had a passport for a year, you have to go through the entire new application process and pay the full fee.
Finally, a lot of people wonder if they can "pre-change" their name in their passport in anticipation of a wedding and honeymoon. Sorry, no. They won't do the change until you have the marriage certificate in hand, which you get after the ceremony is complete. Honeymoon travel has to be done in your maiden name, as far as passport and airline tickets are concerned. Come back from your honeymoon, get your marriage certificate, THEN start the name change process.