If I were you, I'd buy enough from each source - good, fresh DME - and brew two identical batches where the only real variable is the brand of DME. Kind of like a SMaSH beer. Hell,
do a SEaSH beer. Keep it simple. Then taste and see which malt profile you like best.
Me, I'd go with the Briess, primarily because of freshness. Any product coming out of Wisconsin is going to be fresher than product coming off the slow boat from UK.

Besides, I like Briess's products.
But I think you'll have to do a side-by-side to be sure. You could ask 500 people and still get a response diametrically opposed to your taste buds.
So buy some extract and start brewing!
Bob