I someone really wants a recomendation for one bluegrass record, you might consider Red Allen "The Folkways Years 1964-1983".

The old LPs were hard to find, but this recent release has lots of material collected from a number of records.

Fine mandolin work by Frank Wakefield, banjo by either Bill Keith of Bill Kuykendall and an assortment of acoustic bass players. Fiddle on some cuts.