Confu-
I have to admit that I had my mind made up before I even read your original post - a big DEFINITE on the Worldly Girlfriend. However, now that I've read your post, I've changed my mind: I think that you shouldn't have anything to do with either. I don't think you are ready for any type of a long-term relationship, let alone marriage. I'm not trying to diss you or put you down, but nearly every word you write shows me that you don't understand the concept of "love". It is very different than "lust".
When you are in love with someone, you aren't in bed with them thinking about someone else. If you are, then you are engaging in "sex", which is a biological function that dogs, cows, pigs, and goats are just as capable of engaging in as human beings who don't know the concept of "love".
When you are in love with someone, you aren't in bed with them thinking about how great you are at "treating" them, because you know her well enough to know that her idea of being treated well has nothing to do with the bedroom, your money or your looks.
When you are in love with someone, you aren't looking to "trade up" - with or WITHOUT the opportunity to do so. You are satisfied with what you have.
When you are in love with someone, the first things that come to mind when you think about them are the "little things" that make that person unique and special to you - not what everyone else can see just as easily as you can. You put your JW hottie in front of a 75-year old man with one hair follicle and the breath reminiscent of methane, and he's going to see exactly what you see - a 21-year-old "hottie". Nothing else. An object that walks, talks (presumably), and would look just as good in the passenger seat of his Lamborghini as she would hanging off his arm with all his buddies drooling all over her.
Until you've adjusted your perception of "love" (I assume you think you feel that way if you are thinking of marrying the JW girl), you just aren't ready - for her, for your worldly girlfriend, or any other woman, for that matter. You owe it to them and to yourself to mature a bit before you start making decisions like this one.