My favorite ISO 100 BW film is Tmax 100, but I also use Arista Pro 125 (repackaged Ilford FP4), because it's about half the price, and also a darn good film.
My favorite ISO 400 BW film is Arista Pro 400 (repackaged Ilford HP5). Although I am experimenting with Tri-X developed in Diafine, which is supposed to knock the speed up to ISO 1000 or 1250.