I've had Moog "premium" ball joints installed on two different E250's, neither running too close to their upper GVW ratings, they've been flawless but I do keep them lubricated. Originally bought through Amazon, one set back in 2008 and another in 2012, each set with at least 100K miles or more mileage.
I'm disappointed to hear Moog might not be as good as they once were and yes the Dynatrac's are near perfect, fascinating tech that goes into them. But Wowzers on prices---have to think on that as I too am considering preemptively replacing ball joints on my 2005 E350 that is making noise they might be on their out. That van is running close to its upper weight limits so the Dynatrac's make sense but wowzers that cost.
I'll do a bit more reading up on the NAPA/Spicer parts seeing how they fare over the longer term.
Whichever way I do go I want the ability to lubricate them regularly.