I just returned from a business trip that allowed to me eat frozen custard at Milwaukee's Kopp's ( http://kopps-custard.com/ ) , Madison's Michael's ( http://www.ilovemichaels.com/ ) and St. Louis' Ted Drewes ( http://www.teddrewes.com/Drewes.asp ), all within 48 hours. All of these scoop their custard, all are long standing enromously popular local traditions. Ted Drewes is a St. Louis icon. The richest of the three is Kopp's which is 16% butterfat-both of the others are a more typical 10-11%. All three were extremely dense. Both Kopp's and Michael's have unique flavors that change every day Of the three I thought the overall best was Kopp's while the best vanilla was Michael's. For me Ted Drewes was a step below the other two.
I say all this because there is one Washington area frozen custard stand that I believe is as good as any of them: Neilsen's, a Utah outpost, in Vienna. This is similar to Michael's in a 10 to 11% butterfat base and extremely dense. The density allows richness although it doesn't approach Kopp's. Neilsen's weakness are the virtual absense of interesting daily flavors while the Dairy Godmother has flavors similar to both of the Wisconsin standards. I am not a fan of the Dairy Godmother because, for me, it is not very rich. No, scooped frozen custard is not suppose to be but this lacks the the texture of Michael's where, like Neilsen's, it "feels" much richer than it really is.
Carl's in Fredericksburg which uses original ElectroFreeze machines from the mid '50's (one of only two left in VA) is not as rich either although the flavor of its vanilla is excellent.
For anyone who has not tried Neilsen's it may be worth a trip around the beltway. Ted Drewes created the "concrete" and is legendary for it. I think Neilsen's is better. Also, if you hit it on the right day, you may luck out and find one of the few "interesting" flavors they do. Still, for basic frozen custard, sundaes and concretes this is the D. C. area's best and equal-for these-to St. Louis and Wisconsin's best.