This week I installed Hellwig 7008 1.375" front and 7183 1.25" rear anti-roll bars. The recommended part numbers for the E150 are the 1.125" 7604 front and the 7642 1.125" rear bar. Given the pig-heavy front end, I wanted a significantly stiffer than stock front bar. The 1.375" is 50% stiffer than the 1.125", so that fit the bill. My only other rear option was a whopping 1.5" bar, which is 75% stiffer than 1.125", and 20% stiffer than my 1.375" front choice. With a stiffer rear bar I'd run a risk of terminal oversteer, especially if I end up with stiffer rear springs to handle a large towing load. So I stuck with the 1.375" front and 1.25" rear.
(And yes, I know that the differing widths of mounting points makes a significant difference in roll stiffness. Before buying I could only make a rough judgement as to how they differ, and I sure wasn't going to buy and return and buy again!)
Here's the front:
And the rear:
