I've ordered from
http://www.bassguitarstrings.us several times. Fast, and even added some strings to their catalog that I requested, and had them to me across the country in two days.
I've liked the Compressors taper-core B in 36.5 and 38 speaking length, and the GHS Pressurewound B which has 38" of speaking length. I didn't care for the standard-core Compressor B string.
I'd use the GHS Pressurewound if the set is heavy and the KS Compressor taper-core if it's a lighter set.