If you are a survivalist, keep the generator. It won't get knocked out in case of electro magnetic pulse created in nuclear war.
You'll get arguments both ways on this. "Better" is usually the newer product for one reason or another. Otherwise, I would let it be determined by the amount of originality that is important. Both work fine, But if you are going to add a bunch of electrical equipment to the vehicle, you might want to consider alternators.
For a stock truck, I think in terms of "how easy can I fix it?"
A generator is pretty easy to rebuild. I've never replaced a diode on an alternator, but I know I can find a replacement easier. You might want to consider how hard it is to find parts for a generator vs. an alternator. I can go to most parts stores and get an alternator for my 65 chevy.
If it is reliability, I don' t have a problem with either as long as I know up front what kind of shape either is in when I'm starting out.
