ejoachim-
You've probably gotten all the advice you need from this thread and other pilots you've talked to, but I'll throw in my .02 anyway. I say always keep as many options open as possible, so go UPT instead of ENJJPT.
A lot of guys have made the very valid point that you can only find the supersonic, pulling g's, tactical fighter flying in the military, and that if you choose heavies you might regret it later. That's absolutely true. However, it's also true that that type of flying isn't right for everybody. In my UPT class, 25 out of 28 of us raised our hand on day 1 when our flt/cc asked us how many wanted to fly fighters. But 6 months later, on track select day, only about 10 people were still competing for the 6 T-38's in our drop. The rest had decided they wanted to fly heavies because they wanted to see the world, because g forces hurt their a$$, or because they were just too laid back for the intense fighter lifestyle.
If you're being offered an ENJJPT slot, then I'm sure you're smart enough, motivated enough, and talented enough to be near the top of your UPT class and get a T-38 if you still want it. So I say you should get a taste of military flying, talk to lots of IPs with different backgrounds, and give yourself the option to fly any plane in the Air Force inventory. Who knows, you might decide that helicopters are your top chioce.