I have loved Mustangs since I became aware of the differences in cars. I even like the Mustang II's now, especially the King Cobra.
In regards to one over the other...They are both cool.
For a young driver, I would suggest getting a beater for the first 2 years or so. (This in order for you to learn how to actually drive) It is one thing to be a steering wheel holder, and something else entirely to be able to read the road and the other drivers around you. If you have even a somewhat powerful car, and you go throigh your first winter, you have a much higher chance of finding that one special telephone pole!
If you wreck your first beater, it is a lot easier to handle than paying for a car that is sitting in the junkyard...
BTW, a beater doesn't necessarily have to be ugly or rusty or a Yugo...
More to your question, the 1965 model is nice, but the trade-off is found in the price of parts and frequent repairs.
Also, a carb does not generally get any kind of reasonable fuel mileage, UNLESS it is tuned precisely to the engine by somebody who knows what they are doing with it.
Fuel Injection does not have this issue.
Creature comforts are also a big issue for comparisons of the old VS the new.
My 1986 F350 is VERY spartan in creature comforts. So I have to update it, or buy a new truck...
Either option is not cheap.
But it all boils down to what you personally enjoy, as you will be the one behind the wheel.
I also reccomend that you don't limit yourself to these two years. There are MANY good models to choose from.
For me, I would get a '5 1/2 anniversary model. Such as the 30th (1995 1/2) or the 2000 1/2...
I have had several Fox body Mustangs, and loved them all.
Good Luck with it!