Anyone else like low-density, tall/floppier, soft knots?

I agree with you - I find that the super high density badger knots I have don't do as good a job of lathering or painting.  I have some Thaters that I like that have a higher loft and lower density and my Semogue and Omega boars to an excellent job as well especially with soaps like GD Kairos, DG Milksteak and BM Softheart.  I also agree that the Kent brushes perform very well also - the right balance of loft, density and backbone for excellent lathering.